Another question about my biology prelab.....please help.?

This concerns calibrating a reticle on the microscope. Is this correct? If microscope A is 40 reticle units per 1 mm than what is the number of nanometers for 40 reticle units? is the correct answer 40,000 nanometers per reticle unit? This lab manual is the worst at explaining things, and if you get the first part incorrect at the beginning, then the rest is going to incorrect because you need to use the first calculations. ahhhhhh