Totalizing is a kind of integral (find area under curve).
1. You have to sample Analog Input and store samples in memory vector or in data table.
Similar to next:
Where number of sub-intervals is 4, and number of samples is 5.
Sample 0 is at left and sample 4 is at right.
Lets say that this curve is for 30 sec, then sampling interval is 7.5 sec.
*Refer to right trapezoidal drawing.
2. Total T can be calculated as follows:
T=SUM of all ((Sn+S(n+1))/2), multiplied by sampling interval.
*Formula may be optimized for better precision.
Next is a picture where number of sub-intervals is 20, and number of samples is 21.
Making interval smaller make precision better.
Sampling with constant sampling period simplify total calculation.