CPT instruction

I have ran into something I have not seen before and wondering if any one had any ideas.
The logic I'm currently troubleshooting is using a compute instruction for a flow meter register. In the expression they are use using the formula
a/60+ mag meter register. The answer is then placed in the destination. I'm trying to find what is (a)? I'm using a 1756-IF8 analog input card which is already scaled internally through 4-20ma signal and then the low and high engineering 0-400 gpm. Any help would be appreciated. Thx

Guessing:
a is a tag for the flow input (have you tried cross references?), that is used in a totalizer that is updated every one sec. (is this in a cyclic routine?)
Dividing the meter input by 60 gives flow per second, which is added to the total.

Never mind I found the issue. Thank you for the help. When I was looking at the expression I wasn't seeing the whole formula for some reason. You are correct . What it is doing is looking at the IO address/60 + mag meter registration to give you final GPM. One question I would like to know when scaling different instruments where is the best information for scaling formulas?

an algrebra reference ought to do it: y = mx + b