Piston Ring Information

[bikerbob]

I have now bought some different rings from C&D Auotos they say they are made by GPM. I was expecting to get 2 identical compression rings and an oil ring, but on opening the packet the first thing I noticed was there was nothing to indicate which way the rings were to be fitted so assumed wrongly that they could go either way. On further inspection I found that the top ring is a normal compression ring the second compression ring is a stepped ring and the oil ring has a bevel on one edge the step is quite easy to see but the bevel is very small and could easily be missed. Doing a further bit of checking I found a chart that lists quite a few different types of piston rings according to that chart I have a SQ square cast iron ring a DS Step scraper ring and a GBSlotted oil ring,grooved w/bevel cast iron. I have included a copy of the chart I did not realise how many different types of there are.
I also on researching GPM rings found this on  the Draganfly website I have copied and pasted the paragraph but am struggling to understand it. I thought that if you measured the piston ring gap in an unworn part of the bore and the in the most worn part of the bore then  took the difference that would tell you how much wear there is in the bore what has pi got to do with it.
                                                                             (Piston ring gaps are frequently quoted as a method of ascertaining bore or ring wear. When using this method, the ring gap should be measured near the top of the bore and compared with the gap obtained in the unworn section of the cylinder at the bottom. Divide the difference by Pi (3.142) to obtain the amount of wear on the cylinder. The figures that are given for ring gaps are the minimum in order to prevent the rings closing up when they expand, a larger gap, within reasonable limits, is not detrimental. Some of the re-manufactured rings do have a larger gap than would normally be expected. The piston clearances are listed below. All pistons are complete with rings, gudgeon pins and circlips. 1.0 mm is equivalent to .040".)
I did not use the piston ring method but measured the actual bores I have .003" maximum wear at the top of the bore.