This is a special instrument. Both in term of construction as well as personally. A long time ago, when looking for a sextant to aid my teaching I was offered a Skalen sextant. However, after testing it, I found out it was broken and then went on to the classic Freiberger instead. Many years later I have been regretting that decision and vowed to get one at some point in time. Not because it is the best sextant in the world (it isn't) but because it is the only sextant that crosses the divide between geodetic instruments and sextants.

Just like a Wild theodolite, this sextant has a glass scale which is attached to the index arm and thus moves along a fixed prism which then diverts the light towards a microscope. The microscope has a fixed minutes scale along which the degree scale seems to move. Half minutes can be estimated but that is about it. Although a simple design it is less accurate than some of the drum sextants. The advantage is that the scales on the glass can be etched very accurately (if done correctly).

To light up the glass scale a small window is located on the front of the instrument. For dark conditions a separate light source can be mounted. Unfortunately the original light system did not come with this sextant but a test with a flashlight was very promising in that respect.

This instrument never became very popular and as such is a rare find. This specific one had been tampered with as both the index mirror as well as the telescope were not original but replacements from a regular (and later) Freiberg sextant. I replaced those with items from a period correct Freiberger for the photographs but now have either a regular Freiberger or the Skalen sextant without the proper fixtures until I can find a donor.

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Sextantbook