Using 2 apps for tracking- showing different amounts of tirz in my system ?

I searched the sub but didn’t find anything. Sorry if this has been asked.

I use 2 apps for tracking my shots. The one in the Rift Portal & one called Dr GLP1. I was doing this to figure out what one I like more. Anywho, I have logged the same shot dosages & same days on both apps. But the amount of GLP in my system does NOT match on the apps.

Has any one encountered this? Do different apps use different methods for calculating how much is in your system? If so, what app is most accurate?

Thanks in advance 🙂