Looking for some feedback / thought on Shewhart charting different measurement systems. Which one would be best if any?

A little background. We are a measurement / inspection lab so the product we “make” is dimensional measurement. I am tracking the performance of all of our measuring instruments to each other by using the normalized error method (error / expanded uncertainty). This gives a graph of tests over time that should remain between 1 and -1.

I would also like to track the individual measurements over time and show if the measurement process is acceptable. We rarely measure the same part more than once as each project is for a different client with different needs. This is where the question comes in. I am currently leaning towards an I/MR chart but wanted to elicit thoughts from all of you as well.