Which test? Comparing to instruments

I used to feel pretty good with statistics, but it has been a few years. I need help understanding the best test and how to set it up.

I have a data set from two instruments. Each instrument says it measures +/-15% of actual, 95% of the time. I have different test parts which have each been measured once by each instrument. The ‘actual’ value is unknown. How can I analyze if the two instruments read the same (within the expected +/-15%)?