Hey tonz are you looking for inside micrometers???
outside micrometers??
micrometers (inside) will measure the inside of a curved object and assist to find the centre.
If you are measuring a bushing or sleeve they are epic?
they work well in cylinders of all descriptions it is however important to measure on 4 axis to ensure no ovality has occured
Ie 12 o'clock 2 o'clock 4 o'clock 8 o'clock and 10 o'clock , measurements should all remain same throughout length of cylinder..
alternatively if if you aren't trying to measure more of a bowl sort of shape same again but providing lip of said bowl is flush ( level and machined true) you can set size and rotate whilst getting measurements to the lip right around.
They are super pricey for a one off job, can be hired but it may be cheaper to make a jig up instead if it is a uniform measurement???
be careful on what metal you use to make a jig, in a pickle and to check for expansion on things like bearings and couplings it is best to utilise a welding rod , cut to size so it just fits inside bore. Once item has heated for expansion ( no more than 120 Celsius if bearing or steel, no more than 50-60 if bronze but check with manufacturer of bronze due to lead composition) use welding rod as go/no go gauge if it drops through molecular expansion has occurred now fit item quickly prior to cooling.
If I am talking hieroglyphics please provide further detail on project