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David ,

This a Fuller circa 1920s-60s. the image is a bit blurred, so cannot be sure what is on the inner tube. Looks like data but no log or sine scales. therefore a type 1. If you can locate the serial number, I may be able to date it. The mark 2 had log and sine scales on the inner tube and therefore better for celnav.

I have a type 1 original from my grandad circa 1940-50. main advantage was great accuracy due to the length of the scales.(4-7 decimal places)

I have used mine for celnav., but built several modified copies for taking to sea (original too precious). Details on request. My latest Fuller 3 has sines, cosines tangents and can do all the main celnav equations easily.

These days I tend to use the Bygrave for LOP and  basic altitudes and great circles and the Fuller 3 for most other things including lunars..Works great and you  do not need reduction tables or logs.

I should try to rescue it from the window ledge. They do not like prolonged exposure to sunlight and heat. The scales might well be distorted by prolonged exposure.

I've done loads of work on these over the years if you need anything in particular. try to get a detailed picture and serial number for accurated identification.

Best wishes

Francis