This instrument is graduated as a land survey / geodetic instrument in 175 gon rather than degrees. The equivalent is around 155 degrees in the more customary 360 degree system. The instrument is equipped as a 'true' survey sextant with a set of additional legs to put it up side down when not measuring as this makes it easier to lift it back using the handle. It also has the optional 90 degree (100 gon) prism extending the angle from 0 to 175 upwards to 100 - 275 (or 245 degrees). The instrument differs from my other C.Plath survey sextants in that it does not have a drum but is of the 'Heath - Hezzanith' type. That means it has a worm for fine adjustment but still uses a vernier (called nonius by C.Plath) to read the angles. The vernier can be directly read to 0.2 gon.

The instrument is a former Rijkswaterstaat instrument and used to belong to the central geodetic service ("Meetkundige Dienst"). This is not shown but I found this out through its rather shady history. The instrument was put into a web based inventory as belonging to the Rijkswaterstaat inventory of instruments. It was presumably stored somewhere for future generations. I was unaware of this when the instrument came up for sale on the internet. As it is a special instrument I obtained it from a lady who had inherited it from her late father. How he obtained it she did not know. It can be identified as the same instrument based on the Rijkswaterstaat internal reference number '109'. Together with this instrument at least one other instrument from the same collection was offered up for sale.

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Hollandse Cirkel