किस मापक यंत्र में डेटम लाइन के ऊपर समानांतर रूप से अंकित अतिरिक्त, समान दूरी वाले वर्नियर ग्रेजुएशन होते हैं?

Which statement is correct regarding calibration frequency of measuring instruments?

A standard Vernier caliper is generally used to measure:

Which type of error cannot be completely eliminated but can be reduced by repeating measurements and taking an average?