A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Douglas Stephen
Date: 2018 May 2, 14:30 -0700
There are currently a couple HP41 Navigation modules listed on eBay.
The numbers pictured on the back of the unit HP 00041 - 14028 is the same as on the Navigation module in my HP41CX which works well. Documentation is available on line.
I really like the module. It is easy to call routines from the module to use in your own programs (for example to the the GHA and declination so that you can make programs for things like time sights, precompute azimuths and HC,...).
I have no connection with the seller, just noticed them on eBay.