How do I measure the interior of a cylinder?

I have a doubt, as I do to know how much it measures the interior of a cylinder, what I need is to know if it is measured for a change of piston hoops or not. I only have one probe and one ring, but I don't remember if with that I can really measure .. Thank you.

You can place a ring inside the cylinder in the central part even and measure with a feeler the distance between tips of the ring, then look for a cylinder sector that does not suffer so much at the top of the block but internal of the cylinder or in the deepest part of the cylinder (if you have the cylinders without the pistons) and repeat the same process, this should not be a distance greater than 0.15mmm One of another , if this is superior you must rectify the cylinder or perhaps aimed to leave it std (but if those measures are superior when rectifying this will tell you if you should leave it STD or if you can pass to the next measure), in the event that the measures are lower you just have to check the cylinders.
The other way is to use an interior comparator clock that is the most accurate.
Well those are the two forms that I know to measure cylinder interior
maybe there will be another way but I do not know

Hello to measure the cylinder diameter you need an easy caliber to get and not very expensive with the nails that it has in the back of the caliber you have to measure it putting them well straight so that you do not error to the extent you have digital ones that are more easy to read a greeting I hope you serve you