help abouth project

[mustafa025]

hi all
ı am new here . ı make a project for a machine . in my code ı use 18f4520
ı meausre temperature with pt100 and flow sensor .
in code ı use timer0(1sn) for time , ı use timer1(10ms) for flow seonsor .
when the code work in real pt100 meausre good but when ı press button which is counting time (ı used time0)
temperature fall 5 deggree when ı close button temperature is ok
what is the tproblem can you help pls
thks

[TheOldGeezer]

Are you using two AD inputs for the RTD and CAL for the PT100?
The 32bit floating math is simple using the PT100 temp coefficient.
What reference voltage are you using? Internal or a fixed external?
If internal, does the PIC Vdd drop any when you push the button?