Calculate Error from uneven rail and reference

[feldah]

Hello and sorry because i allready asked some question about cheaper ways to straighten my linear guideways. But I had an idea where I wanted your opinion on. So in my case I have a linear guideway of 4m but it can also be smaller for my idea. I want to have it as precise as possible. A straight line reference is too expensive for my hobby project. So I had the idea to buy a Granite tile by the size of 1mx10cmx1cm. I won't know the error of it of course. So my idea is by using a dial indicator to align it at 0 on tip (M0) and end (Mn) of the Granite. Now I would take measurements (M_i) every 5 cm. Every M_i will consist of two errors A_i from the Granite and B_i from the linear guide way. So that I could write for the first measurement M1=A1+B1. For the last one I could write Mn-1=An-1+Bn-1. Now when I flip the Granite and align it again to Mf0=0 and Mfn=0. And i would get Mf1=An-1+B1 and Mfn-1=A1+Bn-1. Now I would have 4 equations with 4 unknown. Which I can solve. Does that work? I am aware that you can buy linear reference second hand cheaper. But my question is more of theoretical interest.