Dexascan and Renpho - what do I trust?

SModa61

For starters, as a gift to myself, I finally got a Dexa Scan a month ago, on May 6, 2023. I have always been curious what it might tell me. At first, I came away elated, then later I began to wonder "could it be wrong". I have recently picked up a Renpho travel scale that provides data as well, and not sure they are telling me the same things.

I'd love to get insights from others. I am trying to wrap my head around the data. What do I believe and what do I not.

My background is I am a 61 year old, post menopausal woman. My exercise currently revolves around mostly fast walking or jogging. I am 5'5", and waist is 28" ATM.

DexaFit Scan results:
Date 5/6/2023, 8:20 AM
Weight at the time of the scan was 131 dressed and hydrated (required for the test). (129.4 naked AM home scale which matches Renpho)

body Fat% 28.2/37 lb suggested goal 25%
lean mass 68%/90 lb suggested goal 94 lb
Visceral fat 0.46 lb suggested goal 0 lb
Bone mineral Content: Total 4.70 lb
Bone Mineral Density:
total body 1.18
trunk 0.84
head 2.98
arms 0.77
legs 1.10
ribs 0.65
spine 0.89
pelvis 0.96
T-score 1.00

Renpho Body Fat travel scale: (note, the body weight component is dead nuts)
Date 6/9/23, 7:14 AM
Weight 123.4 lb (naked, no hydration) labeled "normal"
BMI 20.6 "normal"
Body Fat 24.0% (29.62 lb) "health"
Fat Free weight 93.8 lb
Subcutaneous Fat 22.5% "standard"
Visceral Fat 4 "excellent"
Body Water 52.2% "normal"
Skeletal Muscle 44.3% "standard"
Muscle Mass 88.2%/88.2 lb "standard"
Bone Mass 4.6%/5.6 lb "above average"
Protein 18.1% "adequate"
BMR 1298 kcal *see note
Metabolic age 56

* the same day I did the dexascan, I did the RMR test and got an REE of 1469.

Online I then tried to learn more about visceral fat numbers. I used the Luxembourg Institute of Health Visceral Fat Calculator. Put in my numbers and got 83.46 cubic cm of visceral fat. Apparently, you want below 130 cubic cm (optimally, under 100 cubic cm). I converted the cm, to grams of fat, to lb and got 0.0418 lb of visceral fat.

What am I learning from any of these? What do I trust? And that are likely errors (can dexascan be wrong)?

Ironically, as I write this post, I am understanding this all a teeny bit more.

TIA

sollyn23l2

SModa61 wrote: »

For starters, as a gift to myself, I finally got a Dexa Scan a month ago, on May 6, 2023. I have always been curious what it might tell me. At first, I came away elated, then later I began to wonder "could it be wrong". I have recently picked up a Renpho travel scale that provides data as well, and not sure they are telling me the same things.

I'd love to get insights from others. I am trying to wrap my head around the data. What do I believe and what do I not.

My background is I am a 61 year old, post menopausal woman. My exercise currently revolves around mostly fast walking or jogging. I am 5'5", and waist is 28" ATM.

DexaFit Scan results:
Date 5/6/2023, 8:20 AM
Weight at the time of the scan was 131 dressed and hydrated (required for the test). (129.4 naked AM home scale which matches Renpho)

body Fat% 28.2/37 lb suggested goal 25%
lean mass 68%/90 lb suggested goal 94 lb
Visceral fat 0.46 lb suggested goal 0 lb
Bone mineral Content: Total 4.70 lb
Bone Mineral Density:
total body 1.18
trunk 0.84
head 2.98
arms 0.77
legs 1.10
ribs 0.65
spine 0.89
pelvis 0.96
T-score 1.00

Renpho Body Fat travel scale: (note, the body weight component is dead nuts)
Date 6/9/23, 7:14 AM
Weight 123.4 lb (naked, no hydration) labeled "normal"
BMI 20.6 "normal"
Body Fat 24.0% (29.62 lb) "health"
Fat Free weight 93.8 lb
Subcutaneous Fat 22.5% "standard"
Visceral Fat 4 "excellent"
Body Water 52.2% "normal"
Skeletal Muscle 44.3% "standard"
Muscle Mass 88.2%/88.2 lb "standard"
Bone Mass 4.6%/5.6 lb "above average"
Protein 18.1% "adequate"
BMR 1298 kcal *see note
Metabolic age 56

* the same day I did the dexascan, I did the RMR test and got an REE of 1469.

Online I then tried to learn more about visceral fat numbers. I used the Luxembourg Institute of Health Visceral Fat Calculator. Put in my numbers and got 83.46 cubic cm of visceral fat. Apparently, you want below 130 cubic cm (optimally, under 100 cubic cm). I converted the cm, to grams of fat, to lb and got 0.0418 lb of visceral fat.

What am I learning from any of these? What do I trust? And that are likely errors (can dexascan be wrong)?

Ironically, as I write this post, I am understanding this all a teeny bit more.

TIA

Yes, dexascan can be wrong and *is* inaccurate because it can be manipulated by water weight. I can drink a bunch of water, go in for a dexascan, then go home, dehydrate myself, go back, get another dexascan and show I've "gained" muscle mass. There are cases of instagrammers pretty clearly appearing to do this to sell products. And people believe it because they got a dexascan done, so it's got to be true!". Basically, at the end of the day, just trust what you see in the mirror and how your clothes fit.

tomcustombuilder

Look in the mirror. How do you look? Too much fat? Lose it. Too thin? Add weight.

I’m just not a fan of any of those machines. You don’t walk around with your BF numbers on your shirt however your body composition is apparent just visually not to mention the inaccuracies of the scales and to a lesser extent the DEXA.

Everyone carries fat differently so 20% on one person can look completely different on someone else.

Those places that have the DEXA SCANS make GOOD money from em so of course they tout the “benefits” and why they’re necessary.

SModa61

Thank you both @sollyn2312 and @tomcustombuilder for your replies.

Tom, I would agree with you totally if my interest in the data were appearance based, and to a degree I do do that. That said, the mirror will never tell me the condition of my bones, which is of interest to me as a 10 year post menopausal woman. Visceral fat AKA the bad fat is purportedly less able to be assessed by just the mirror, or so some claim. The other numbers are just more "interesting", but if reproducible by the device then its an additional way to measure improvements. I do do bi-weekly measurements, which are now not as interesting as I am trying to maintain current weight so number changes are rare.

Sollyn, If proper instructions are given and followed by the user, shouldn't at least certain numbers be accurate?

One more comment about a mirror assessment. Two pregnancies destroyed the skin from above my belly button on down. This does make the mirror assessing more difficult. I will never be able to have visible abs, which I am OK with.

ninerbuff

IMO, the easiest way to figure out if your too fat is just to pinch. Certain people may have thicker skin, but a pinch test will give you an idea. If you pinch area of your body that have little fat (back of your hand, around your forearm) you can tell the thickness of fat compared to say your waist, or hip. Pinching more than a inch would indicate you'd have some fat to lose.

A.C.E. Certified Personal and Group Fitness Trainer
IDEA Fitness member
Kickboxing Certified Instructor
Been in fitness for 30 years and have studied kinesiology and nutrition

SModa61

@ninerbuff Wouldn't that apply solely to subcutaneous fat, and not visceral fat? Also, what about bone density? But yes, I remember that age old pinch test.

chris_in_cal

SModa61 wrote: »

(can dexascan be wrong)?

Of course it can. It is the best currently available tool. When used in good faith you can have very high confidence in it.

Seeking, analysing, acting upon data can be powerful. It is how we have science and Western civilization.

Truth, is a different subject.

Do you have a pinch, do you look good in the mirror, disbelieving measurement tools are all subjectively fine. Analysing data is fine too..it is just a different discipline that doesn't appeal to everyone.

SModa61

@chris_in_cal I love data. Don't know why, but I love it. So far, most responses have referenced the mirror. But the data that is given, goes beyond just the mirror. It includes bone and visceral fat info. Both of those are supposed to matter to us.

On another note, a friend in another group suggested I use the Navy body fat calculation. That came back as 23%. Different from both of the above.

AnnPT77

Dexa is the best available way of assessing bone status, IMU. For example, it is the test that's on repeat for me, after having been diagnosed osteopenic (and I think now actually osteoporotic).

The home scale, even a good one, is really not a precision instrument for assessing body composition. If it's just a stand-on model (without separate hand contacts) it's even more iffy. Dexa, while not perfect, should be better.

Reading your numbers, it doesn't seem like they're really far enough apart to be deeply worrying, but I know that's pretty subjective. (FWIW, I'm close to your size, 5'5" (and shrinking 😬), 130-point-something pounds this morning, I figure from various measures around 25% BF +/-, and age 67. So, although that's a subjective comment, it's at least coming from a nearby demographic, if that matters.)

I'd add this: If you're worried about bone quality . . . all you can reasonably do is all you can do. Strength and other exercise, good nutrition (especially things like calcium and vitamin D), avoiding bad habits (excessive alcohol among other things) - you can easily research osteoporosis avoidance lifestyle measures, and adopt them to the extent practical (and I do mean "practical", not "obsessively").

You may be recommended meds if osteopenic, and have to consider that. If so, ideally you'll have specialist medical advice. (I took bisphosphonates for around 4 years. No problems, no big deal, saw improvement; specialist approved going off them. I may need to go back on, that's still up in the air.)

Just my opinions throughout, though.

springlering62

@SModa61 I am your weight loss twin. I am 61, too, have lost a large sum of weight, am very invested in keeping it off, and building muscle. I also dwell on numbers and thrill to graphs.

Like you, I’ve got a Renpho scale and have done DEXAs.

Don’t be too invested in these. I’ve had three, on my first second and third anniversary of beginning weight loss, and am not having any more.

I deep dove and gnawed on the results, sobbing over my “failure”, beating myself up, too emotionally invested.

Look, I’m 61, I’ve lost from 22w to a size 4, that’s really all I need to reassure myself I’m on the right track. It took a few days to “let go” the DEXA results and tell myself “dang girl, you’ve done all right. Chill!”

In retrospect, I feel like a total chump for letting it dictate and get next to me like that.

As far as the Renpho scale, I assume you’ve got the Bluetooth app. Go back and look at trends. It’s so inefficient and inaccurate that some of the graphs are downright laughable.

Also, and this is my humble opinion, I think the DEXA can return odd results for those of us who’ve had large weight loss. It says I have a large band of visceral fat, when I’m pretty sure my core kicks *kitten*, but boasts a floppy ring of what is simply extra skin. There’s not many of us who’ve experienced that kind of weight loss (go, us!!!!) and I honestly don’t think it’s been calibrated or scientifically set to deal with that.

Unless one of us is planning to compete in weightlifting or body building (as if!!!!) mirror results are the best, along with the occasional new personal best for speed, distance, barbell or dumbell attained.

Hug and congratulate yourself. You’ve killed it!

PAV8888

I would look carefully at the suggested goal numbers and who and at what age they are suggested for and independently cross reference them

Also +1 t-score is pretty good bones, right?

Also your machine model should be in the results and can be looked into for error

Also glycogen water and food can all afect dexa independently of the machine error and interpretation/operator error (because a person places the little dots). So more than just one error.

And the bio impedence scale is great.... in being able to tell you that everything goes down or up randomly when your non calibrated weight goes up or down.... at least the weight thing tends to be ok when not playing with fake consistency 🤣 (I e. It's like a fortune cookie)

I did multiple dexa scans and found them interesting, motivational even and ultimately utterly inconsequential other than for their entertainment value one exception being they validated slowing down weight loss a little bit earlier than I would have otherwise. But given the numbers I don't see your as being in a rapid loss phase anyway so think of them as a fallible and manipulatable data points with large discrepancies worth a second look as to why they might be there.

cwolfman13

DXA is the gold standard. I've never seen "places" with a DXA, only medical facilities and the procedure is done by a radiology technician. It also provides way more beneficial information than just BF%, particularly when it comes to bone health.

chris_in_cal

SModa61 wrote: »

@chris_in_cal I love data. Don't know why, but I love it.

My 8 year weigh chart, and my 30 year blood lipid panel results are some of my most prized possession.


Geeks unite!

springlering62

cwolfman13 wrote: »

DXA is the gold standard. I've never seen "places" with a DXA, only medical facilities and the procedure is done by a radiology technician. It also provides way more beneficial information than just BF%, particularly when it comes to bone health.

You can buy DEXA scans at “places” on Groupon here (Deep South). I’ve been to one in an RV kinda rig that goes from gym to gym fitted with a scanner, and two in a bare bones two-room suite in an office building of mostly lawyers and CPAs. A sofa in the waiting room, and a small desk and chair and scanner in the other. And a couple of bog standard inspirational posters of athletes for decor. One in each rather depressing room.

That’s all they do, day in and day out- feed our insecurities, or securities, as the case may be. 😜

PAV8888

Used machines exist in the open market and quite often people with radiology training or even full radiologists are the ones running them. But the operator's choices, versions of software and whether the machine has been calibrated or not and is properly maintained or not do have some relevance

Ultimately though, whether you had one or 10 cups of coffee, a refeed day or a 2 hour run the night or morning before your scan and whether you scan under similar conditions the next time (let's not even forget a high sodium meal) all these things will play into the results

But even more so the narrative that accompanies the results comes into play.

If I recall correctly 61-year-old female? I sort of question the 25% aspiration printed in the results which frames the narrative more so than the results themselves

My first AI assisted Search came up with 24 to 36% being the healthy range for a 61-year-old female and below 24% being under fat

Sort of frames the listed 25% target somewhat differently, doesn't it?

tomcustombuilder

Just to be clear on DEXA bone scans, they read area and not density so a smaller boned, good density person will get a lower reading than a larger boned person with lower density. This is how it was explained to me awhile back.

Now, if the same person got a reading and went back a year later and the reading showed a declining area then I'd imagine that would be a good gauge of how you're doing bone wise

middlehaitch

Hi @PAV8888, for my own curiosity, if you have a link for the women’s over 60 fat recommendation could you post it please.
As you know, I’m a little thing, older, and would guess my fat levels are below/ borderline under. I had read eons ago that the higher fat for older folk was more a protection in case of illness with lack of appetite and that had now been reversed and we olders could have a healthy lower fat level just like the youngers. (Can’t find my link it was so long ago)

@SModa61, I get your quandary on which results to heed. If it were me I would note the dexa but follow the results over time of my bells and whistles scale. You have that on hand and can track over time in the same conditions.

If numbers, over time, were looking like they were going in the wrong direction for bone, muscle mass, visceral fat, and anything else you find applicable, make an appointment with your doc for a full work up including bone scan.

Unfortunately dexa scans have been reduced to toys by the way they are administered for the general populations curiosity.

Personally, being the opposite of a data geek, I’ve relied on movement and nutrition to assuage my worries on bone and muscle health. Still strong, not shrinking, yet, and no medications needed. (I do take D and B12 just in case)

Cheers, h.

SModa61

@AnnPT77 I have thought Dexa’s were as you described and highly respected. Yours were likely performed by medical professionals. Mine was of the type that @Springlering62 has done (I used DexaFit). Mine was done in a simple office setting, and IMM the machine was the machine. You lay in it. It reads you, and that is that. My results were actually really good IMO and I was excited initially, but then your mind gets going. Note that for *kittens” and giggles I paid for their software analysis that predicts certain things. Says I will live to 95 and gave me an A+ amongst other predictions. (New worry, will I outlive our money :P )

So, IF the bone info is accurate, then yay! My bones are really good. I just need to be smart and keep them that way. If wrong then, what was the point of the test. Also, it claimed my visceral fat was good. Another yay! Are these the types of numbers that Dexa tends to get right, or wrong. @Sollyn2312 above pointed out that certain aspects can be manipulated.

@AnnPT77 I appreciate the comparative demographics. I know that you are highly athletic, compared to my dabbling. If you are at 25%-ish, I am certainly higher as I will expect you have more muscles than I.

As for calcium and vitamin D, I am not doing currently as, from my recent reading one wants K (likely K2) in the mix. Argh. Gotta get on this. And as for osteoporosis meds, I have heard that “density” increases but bones become brittle and lose their necessary flexibility which adds a different concern.

@Springlering62 Guessing the “62” in your name means I am a little bit older than you. I was born in 61. What an amazing weight loss you have accomplished. If I recall, Ann has a notable loss as well. My “high” was 168.8, but I am a repeat offender (need to change that), so I likely have lost an awful lot of weight over the course of my lifetime. Funny we both like data. The difference is I am afraid mine is “too good” and therefore false. If it is accurate, I am happy, but if not, then I don’t want wool pulled over my eyes and lead me to making wrong choices. I have only had the Renpho for about 10 days. I bought the travel version solely for its weighing ability (going to Scotland in the fall). Only after I received it, I found it did “other things” and that opened a second can of worms. Sounds like you have a bit more damaged skin than me. Mine is elephant style but fairly immobile. My other annoying skin area is underarm/armpit-ish area. This recent getting my weight down, seems to have increased that. :’(

@PAV8888 Good point on the suggested target numbers. While the target numbers don’t seem to mention an “age” to them, the “analysis” does. For instance, Body fat. The Dexa states Body fat total is 28.2% and 37 lbs, and that I am 22% under the average for my peer group, but suggests that I aim for 25%. It does this for 8 categories. On bone, the give the data with the t-score. I requested additionally my z-score, and that was in the master data, which they also gave me (upon request). And yes, if accurate, I will be very happy with a 1.0 t-score.

I see no reference to machine model in any of the provided reports. I wonder if this is given in the medical setting, vs companies like DexaFit. Also, no “dots” were placed. I don’t recognize what that might be.

@PAV8888 If I am reading between your lines correctly, if sounded like maybe you think mine might be in a correct general ballpark?

@Cwolfman13 – Yes, mine was done through DexaFit. There are a variety of companies out there now that provide this service. Price point is reasonable enough, IF the data has value.

@chris_in_cal Yup, my lipids were not what I expected this year. That is another deep dive area for me as well. I may be paying for some private pay lipid panel re-checks before next year. Was also thinking about an APoB test. And yes, Geek is a wonderful word. I think we are great!

OMG you guys are great. More replies before I got my response together. To be fair, I am multitasking in the kitchen. Hubby and my dinner and now cooking for very pregnant daughter.

@PAV8888 Interesting insights into the machine. I did feel like the process was quite quick. I actually more questioned (after the fact) my REE calculation. Yes, I had been inactive, no caffeine, and fasted, but he put me straight away on the machine despite my just having walked in. Shouldn’t I have “rested” a bit before being measured. That in itself is making me “wonder”. As for the 25% rec, I have no clue, but that is a great point you all have brought up.

@Tomcustombuilder Given that Dexa scans, in the medical setting, are used to actually evaluate for osteoporosis and osteopenia, that sounds like it would be useless if only measure “size” of the bones. But I do agree that evaluating over time and noting change is very valuable. My PCP states I will be given a scan at 65, unless I demand one early. I’m willing to wait for the medical one.

@middlehaitch I had heard about the benefit of extra weight claim as well (I think its my mother-in-law saying it). At the same time, I see the detriment of weight on mobility. As for lack of appetite, that would be a miracle for me. I doubt that is a risk for me any time soon. I appreciate your insights on how to use these tools. As for supplements, I have been researching what I want to add for those. (Thinking D, K2, along with others)

Ha, finally caught up. Will post, then back to the stove!

tomcustombuilder

SModa61 wrote: »

@AnnPT77 I have thought Dexa’s were as you described and highly respected. Yours were likely performed by medical professionals. Mine was of the type that @Springlering62 has done (I used DexaFit). Mine was done in a simple office setting, and IMM the machine was the machine. You lay in it. It reads you, and that is that. My results were actually really good IMO and I was excited initially, but then your mind gets going. Note that for *kittens” and giggles I paid for their software analysis that predicts certain things. Says I will live to 95 and gave me an A+ amongst other predictions. (New worry, will I outlive our money :P )

So, IF the bone info is accurate, then yay! My bones are really good. I just need to be smart and keep them that way. If wrong then, what was the point of the test. Also, it claimed my visceral fat was good. Another yay! Are these the types of numbers that Dexa tends to get right, or wrong. @Sollyn2312 above pointed out that certain aspects can be manipulated.

@AnnPT77 I appreciate the comparative demographics. I know that you are highly athletic, compared to my dabbling. If you are at 25%-ish, I am certainly higher as I will expect you have more muscles than I.

As for calcium and vitamin D, I am not doing currently as, from my recent reading one wants K (likely K2) in the mix. Argh. Gotta get on this. And as for osteoporosis meds, I have heard that “density” increases but bones become brittle and lose their necessary flexibility which adds a different concern.

@Springlering62 Guessing the “62” in your name means I am a little bit older than you. I was born in 61. What an amazing weight loss you have accomplished. If I recall, Ann has a notable loss as well. My “high” was 168.8, but I am a repeat offender (need to change that), so I likely have lost an awful lot of weight over the course of my lifetime. Funny we both like data. The difference is I am afraid mine is “too good” and therefore false. If it is accurate, I am happy, but if not, then I don’t want wool pulled over my eyes and lead me to making wrong choices. I have only had the Renpho for about 10 days. I bought the travel version solely for its weighing ability (going to Scotland in the fall). Only after I received it, I found it did “other things” and that opened a second can of worms. Sounds like you have a bit more damaged skin than me. Mine is elephant style but fairly immobile. My other annoying skin area is underarm/armpit-ish area. This recent getting my weight down, seems to have increased that. :’(

@PAV8888 Good point on the suggested target numbers. While the target numbers don’t seem to mention an “age” to them, the “analysis” does. For instance, Body fat. The Dexa states Body fat total is 28.2% and 37 lbs, and that I am 22% under the average for my peer group, but suggests that I aim for 25%. It does this for 8 categories. On bone, the give the data with the t-score. I requested additionally my z-score, and that was in the master data, which they also gave me (upon request). And yes, if accurate, I will be very happy with a 1.0 t-score.

I see no reference to machine model in any of the provided reports. I wonder if this is given in the medical setting, vs companies like DexaFit. Also, no “dots” were placed. I don’t recognize what that might be.

@PAV8888 If I am reading between your lines correctly, if sounded like maybe you think mine might be in a correct general ballpark?

@Cwolfman13 – Yes, mine was done through DexaFit. There are a variety of companies out there now that provide this service. Price point is reasonable enough, IF the data has value.

@chris_in_cal Yup, my lipids were not what I expected this year. That is another deep dive area for me as well. I may be paying for some private pay lipid panel re-checks before next year. Was also thinking about an APoB test. And yes, Geek is a wonderful word. I think we are great!

OMG you guys are great. More replies before I got my response together. To be fair, I am multitasking in the kitchen. Hubby and my dinner and now cooking for very pregnant daughter.

@PAV8888 Interesting insights into the machine. I did feel like the process was quite quick. I actually more questioned (after the fact) my REE calculation. Yes, I had been inactive, no caffeine, and fasted, but he put me straight away on the machine despite my just having walked in. Shouldn’t I have “rested” a bit before being measured. That in itself is making me “wonder”. As for the 25% rec, I have no clue, but that is a great point you all have brought up.

@Tomcustombuilder Given that Dexa scans, in the medical setting, are used to actually evaluate for osteoporosis and osteopenia, that sounds like it would be useless if only measure “size” of the bones. But I do agree that evaluating over time and noting change is very valuable. My PCP states I will be given a scan at 65, unless I demand one early. I’m willing to wait for the medical one.

@middlehaitch I had heard about the benefit of extra weight claim as well (I think its my mother-in-law saying it). At the same time, I see the detriment of weight on mobility. As for lack of appetite, that would be a miracle for me. I doubt that is a risk for me any time soon. I appreciate your insights on how to use these tools. As for supplements, I have been researching what I want to add for those. (Thinking D, K2, along with others)

Ha, finally caught up. Will post, then back to the stove!

wow amazing responses. So professional. You must be some type of mega organized person. I say that in the highest regard and respect.

PAV8888

middlehaitch wrote: »

Hi @PAV8888, for my own curiosity, if you have a link for the women’s over 60 fat recommendation could you post it please.

in spite of a variation to the exact question bing threw this reference at me both times: https://dexascan.com/guide-dexa-scan-results/ The fat % in a dexa scan may be different than from BMI so both my questions contained dexa derived and 61yo f

PAV8888

@SModa61 I did mine at Bodcomp imaging in Vancouver back when Peter (who both trained and worked as a radiologist) was running it as a one person shop. It was a machine he bought used but he was also maintaining AND calibrating periodically.

There were two settings to his machine depending on whether he was performing a while body or bone density scan. A whole body also gives a basic bone density figure. But for the "medical bone density scan", he set the machine to greater depth / stronger emission and also concentrated much more on the pelvic area and hips. Source: my mom got jelly and wanted a body comp scan for herself and since we were there and Peter was qualified to interpret the scan she also asked him to perform a full bone density scan.

The dots are literally dots on the screen. At least on that (older) version of software the operator, once the scan was complete, had to define (select, approve, or modify) on the image on their screen certain parts of your body so that the machine which know which areas to use for the various calculations. For example the bottom of your crotch and the tips of the shoulder bones (if my eye and I are remembering correctly) can be placed correctly or even a pixel up or down or to the left or to the right could change the calculations, especially when comparing between runs. This is complicated by exact body positioning which again can differ slightly over multiple scans (neck and foot tilt for example)...