As discussed on my Graphometer - Semicircle webpage, the French produced a good number of Graphometers from 1600 to about 1850. And a fair number of these Graphometers are still around. If you want to add a really nice Graphometer to your collection, this Bion merits serious consideration for these reasons:

1. Bion was a highly skilled maker well known internationally for both his instruments and his book relating to instruments, which was published in French, German and English. Bion's instruments will always be highly collectible given his name recognition.

2. The President of Harvard College in the mid 1700's owned a Bion Graphometer and used it to survey around Harvard. This makes for a nice story if you display a Bion Graphometer.

3. This Graphometer has a really nice design and exhibits a high level of engraving skill.

4. An instrument with transversals - the concentric circles - adds a lot of eye-appeal and interest to early instruments in my opinion. In theory a surveyor could read angles to six minutes of a degree with this Bion Graphometer. As Norwood pointed out at page 80 et seq. in his 1639 book on Fortifications, the mathematics behind the concentric circles and diagonals approach were fairly complicated, with many makers likely missing the mark. Over time most makers opted to use a vernier system instead of the concentric circle and diagonals system. Again, this makes for a really neat story if you display this Bion Graphometer.

5. This is a full size Graphometer - about 15 inches in diameter. Large circa 1700 Graphometers don't pop up that often. Most early Graphometers are smaller, like my Butterfield Graphometer.

All things considered, I believe this Bion Graphometer is a really nice and highly collectible instrument. I also think it would add a good deal of interest to a display of surveying instruments, especially with the different stories you could tell about the instruments as noted above.

For more information about Bion, please see my Bion Maker Webpage.