Although the A12 bubble sextant (strictly speaking, an octant) was a good deal simpler than most other bubble sextants, there are still plenty of pitfalls for the inexperienced. In my latest restoration manual I explain the structure of the instrument and how to reduce it to its sub assemblies. I then explain how to service each sub-assembly and put them together again, followed by a section on collimation and adjustment. I reproduce the instructions for use chapter from the original manual as an appendix. There are over 50 colour photographs and diagrams in a total of 57 pages.
If you would like to buy this manual, it is available as a down load for US$18.50 or for $4 extra, I can post it to you on a CDROM. Make payment through PayPal, using my e-mail address as the payee : engineerATclear.net.nz (where At represents the @ sign) or Contact me.