3.13.6　Analysis and questions

(1)In the experiment,what do you think is the key to adjusting the spectrometer?

(2)What are the similarities and differences between the reading of the double vernier and that of the vernier caliper of the spectrometer?(https://www.daowen.com)

(3)How to assure that the telescope is perpendicular to both plane A and plane B of the plane mirror before the measurement?