1. The problem statement, all variables and given/known data

4 temperature measuring instruments were compared. readings were taken at 10 points (as temp was increased)

2. The attempt at a solution

the wording of the question is what's confusing me. Is each instrument going to have one value for deviation? Or is it asking for a deviation at each reading?

You have four sets of data, each with 10 points? (One for each instrument)

If so, then each instrument will have a standard deviation which you can calculate using one set of data's 10 points. (There should be a formula you can use)

I thought about this, but it says "determine the deviation of each device from the gas thermometer". I could just calculate the standard deviation, but that doesn't compare it against the gas thermo.