NavList:

Aye, tis indeed a wee thing.  But something interesting has come across my mind.  each mirror only has two shades each with which to buffer the brightness and effects from the sun (or other extremely bright object).

This seems odd, considering too that the characters embossed on the arc are roman and not kan'ji.  This suggests to me that yon sextant was a western import.

But two shades, where the standard has always been three or four, that perplexes and amazes me.