IMPORTANT: AVOID ANYTHING MADE FROM BRASS (see below) IF YOU WANT A FUNCTIONAL INSTRUMENT

The pocket transit was designed in the late nineteenth century as a highly portable surveyeing tool for geologists and land surveyors. The instrument is called a transit, rather than a compass, because of the ability to measure both horizontal  and vertical angles. The main features are:

--a bull's eye level for ensuring that the compass is held level,

--a high-quality sighting mirror with a precise vertical line etched in it, mounted on the inside of the hinged cover,

--a sighting structure with two small circular apertures and a point for precise alignment of  an object with the vertical line of the mirror;

--a hinged sight like the distal portion of the one mounted on the front of the compass, on the proximarl end of the cover/mirror.

There are several ways to use the sighting devices that allow you to read either foresights or backsights while holding the compass at eye-level or at chest or waist level.

--An inclinometer, with its own bubble level, and vertical scale, is mounted on the base inside the case. This was designed for measuring strike and dip of geologic formations and estimating general surface grade. The vertical scale is usually in both % grade and degrees.

--A pinyon gear allows the rose to be rotated up to 90 degrees to set magnetic declination;

--Slotted grooves on the case fit an optional bracket that mounts on a standard camera tripod or a special tripod.

THINGS TO LOOK OUT FOR: A pocket tranist manufactured in 1900 is as useful today as it was 107 years ago, provided it is in good condition.

(1) Needle balance: The main thing that goes wrong with pocket transits is wearing down of the jeweled needle pivot. When this occurs, the needle, which should be precise to about thirty minutes of arc, sticks and becomes inaccurate. This can be compensated for by wrapping some fine-guage non-magnetic wire at a certain spot on the needle to bring it back into balance. It was recently pointed out to me that wrapping the needle in this manner is often necessary when crossing between hemispheres.

(2) Scale type: Pocket transits are made with three differenct types of scales on the compass:

--Most people want a scale in azimuths, 1-360 degrees, like most compasses that you see. If that's what you want make sure it's what you are getting.

--Quad scales go from 0-90 degrees four times around the compass circle and are read as bearings, not azimuths (eg S17W, "south seventeen degrees west").

--Military pocket transits are calibrated in mils, which go from 1-6400. Unless you are calling in artillery in the days before GPS, these compasses are next to useless.

(3) Worn out hinges: The hinge on the back mount should hold the mount rigidly so the objective mirror stays at the angle you place it without having to be held by hand. If the back case flops around when opened, it can be annoying but doesn't really impact the accuracy or the pocket transit.

(4) Cracked mirrors or crystals: These flaws usually only mar the pocket transit visusally but may indicate rough handling of the instrument.

FAKE POCKET TRANSITS: IF YOU WANT A FUNCTIONAL POCKET TRANSIT, AVOID ANYTHING MADE FROM BRASS. Brass "pocket tranists," "mariner's compasses," etc., are decorator items or props only. They are not real tools.  Most brass copies sold on Ebay are manufactured in India, even though they may be advertised from a London firm-- often with quite elaborate pedigree, such as "Manufacturers to Her Majesty the Queen," etc. These appear to have been assembled with about as much care as a tourist shop hooka-- and with toy parts. In my opinion, if you pay more than about $20.00 for one of these things, to put on you bookshelf or desk, you're being taken advantage of!

I recommend sticking to the mainstream manufacturers: K+E, Brunton, Ainsworth & Sons, Zeiss, Lietz, to know that you are getting a quality product. Pocket transits from these manufacturers could last a few lifetimes if properly cared for!

Update: Chinese pocket transits (5/5/07)

Pocket transits manufactured in China have been available throughout Asia, Africa, and Russia for some time and are just starting to penetrate the North American market. These compasses usually have brand names that begin with DQL or DQY and are typically manufactured by the Harbin Optical Instrument Co. or Huwangda electronic plastic products in Shenzhen and are often marketed via Indonesian or Russian retailers. I have no direct experience with these products but they appear to be lower-cost alternatives to American and European manufacturers. Their published specifications and tolerances are the same as those of the Brunton Co.

VINTAGE?

The term "Vintage" gets used very loosely on Ebay with regard to pocket transits and compasses. Often the items described in this way are fairly recent. If you accept the definition of the word as "representing high quality or workmanship of past times" it is fairly misleading, as pocket transit design has not changed in the last century and materials and methods of manufacture have likely improved rather than deteriorated over time.