fitbit sync & negative calories enabled?

wongisms

can someone explain to me how this all works? before i just had it synced to fitbit which helped on days where i wanted to just count how many miles i was walking or if i was reaching the 10,000 steps/day goal. but then today i did my 50 minutes of kickboxing and then the adjustment subtracted like 500 some calories from my 900 calorie burn, and prior to my workout, i had burned like 400 something calories just from walking throughout the day.

im jsut trying to understand how this calculation works and if i should have the negative calories enabled or not as it sorta confuses me on how many calories to eat back now.