The Brunton 8040 compass works, but in my opinion…
The Brunton 8040 compass works, but in my opinion there are much better mirror-sight compasses available (if you like Brunton, before you buy an 8040 just compare the Brunton Nexus 15 or 25 Ranger compasses Brunton imports from Silva Sweden AB).
A problem with all the original Brunton 'optic green' baseplate compass designs I believe is their method of declination adjustment. It's by friction only, not by geared screw, and occasionally slips on my example. Also, the Brunton declination adjustment rotates the capsule in relation to the degree dial, meaning that it must be rotated back to zero each time one puts the compass on the map to read a true bearing.
Other complaints: the compass dial markings aren't engraved and inked, but simply printed onto a kind of contact paper and thus less durable and not as finely readable; there are no proper luminous markings for the needle, compass bezel, or orienting arrow; the compass dial on my example soon became loose and would not reliably 'lock in' a preset bearing as it would easily rotate (a big flaw IMO). Also, the tiny red hash marks on the compass' outer dial (instead of normal orienting lines on the bottom of the capsule used by other models) are inadequate to conveniently orient the compass to true north when placed on a map.
Here's what other sites are saying:
A classic example of a trusty compass, the 8040G is a mirrored map compass with our easy-reading optic green baseplate.
The Brunton 8040G Compass includes all the features you need for incredibly accurate backcountry navigation without a bunch of gizmos that you don't really need. Clean, simple, and accurate, the 8040G Compass has an adjustable declination, sighting mirror, and transparent base plate to make map work easier. As an added bonus, Brunton gave the 8040G a built-in thermometer to provide accurate bragging rights on dead-of-winter or heat-of-summer trips.