As shown below, I measured the gross flow of five wells (P, Q, R, S, T) with
the aid of three different measuring instruments (A, B & C). How can I use
excel to accurately predict A4, & A5 (The missing gross flow when I used
instrument A)?

A sample calculation / programming on how excel spreadsheet can be used will
be appreciated. I have tried trend.
Measuring Instruments
"Well #" A B C
P 44.9 46.4 67.3
Q 50.9 52 49.5
R 570 507 574.9
S A4 91.4 72.5
T A5 493.4 369.1

Thanks in advance.

Best regards,
Elijah.