NavList:

Thanks for the link.

I am not seriously considering having the sextant  restored. I am interested to know what it would cost but suspect that it would be cheaper to buy a new metal sextant (-;

I have decided that my project can be split in two distinct parts. First there is measuring Ho. This could be done with the vernier sextant or maybe a second hand Davis Mk15 which would be more than adequate for my needs. In the southern hemisphere it is only eight days to the winter solstice yet ouside there is a clear sky, no wind and a mild 11 deg C. I spent the afternoon adjusting IE and taking sights with an artificial horizon (dish filled with water). I also used a phone app to record the sun's altitude. The next step will be to analyse the results and see how closely my measurements agree with the app (probably not very well!)

The second part of the project can proceed separately. It involves reducing the sights by various techniques.  I propose to use an app to  determine Ho, Z and time for the sun in my backyard. The app I am using does not give any information on the formulas or almanack algorithms used so I will have to take it on trust. I will then pick an assumed position that allows me to use pre-computed tables. I will  determine the intercept by phone app; trig calculator and cosine formula; AP3270 (yes, I purchased the  correct version); HD486 (HO214?) and finally haversines from Norie. I also have ABC tables but OTTOMH I do not know if they can be used to determine intercepts.

This is the type of project that I will probably get very enthusiatic about for a while and then do nothing for a long time. It must be nearly 50 years since I last used mathematical tables so I am dreading  using haversines. To put things in perspective the HP35 calculator went on sale not long after I started work. Not only did it make my slide rule obsolete but it must have changed sight reducton for ever.

Finally, near home is a 345m hill  I often walk up for exercise. If I take the sextant I can measure some horizontal angles as an alternative way of determining my location.