Purposely... explanation is with very slow pace... and with very simple language... If in any doubt... Recommend you to refer my Book titled "Metrology and Measurement", Tata Mcgraw Hill, (International edition).
Your tools are beyond comment Apparently you are in a school setting Cleanliness is of the up most importance If your teaching you should be endorsing Cleanliness is the first step of inspection
Respected sir, what if circular scale reading is not exactly matching with horizontal line of main scale reading....we need to consider upper or lower line on circular scale....
As said here.... lower line is crossed hece related dimension readin is required to be considerd & read horizontal scale. And how much more distance [in micron] you can read using circular scale. I hope answered.
