Cylinder bore inspection

To gain experiance with the dial bore gauge I decided to characterize the engines I have the heads off.

standard min 2.4990"   max 2.500"
Crankshaft is along the '2' axis

 dial reading     adjusted     

A1  -0.0005      2.5025
A2   0.0000      2.5030

B1  -0.0010      2.5020
B2   0.0000      2.5030                 

C1 -0.0015      2.5015            

C2 -0.0003      2.5027

2.4" anvil with .12" washer

Briggs says:

If the bore is more than .003” (.08 mm) oversize, or
.002” (.04 mm) out of round on cast iron cylinders, or
.003” (.06 mm) out of round on aluminum cylinders, it
must be resized, or see NOTE below.

The bore has reached but not exceeded the wear limit in the  '2' direction.

This is an aluminum cylinder so the larger out of round applies.   The worst level is level C at ( 2.5027" -2.5015 ")  or 0.0012".   This is not quite half of the allowed  003" allowed.

In the 2 direction we have a taper from bottom to top.   According to Oklahoma State "Taper in the top half is cause by dirt ingestion through the air filter. Taper in the bottom half is caused by dirty oil.

This is all based on trusting the digital micrometer I am using.  Would be nice to have some way to check it.