I switched from a simple Suunto A10 base plate compass to a Brunton 15TDCL Sighting Compass last year because I wanted a compass that was more robust for bushwhacking, backpacking in open country across Scotland, and for avalanche prediction in New Hampshire’s White Mountains.
While the A10 has been an old friend, I felt that the Brunton had some more advanced capabilities that would provide me with a higher safety margin and would push me to become more adept at advanced route finding. I was right, it did.
This particular compass is considered a classic by many. It’s most obvious feature is a folding mirror which collapses down over the bezel when not in use. That’s a handy feature for keeping your bearing set if you’re walking across open country. In addition, the 15TDCL has metric and non-metric rulers, 1:24,000 and 1:50,000 map scales, a magnifying glass, 2-degree graduations, rubber feet, and a lanyard hole. The Brunton weighs 2.6 oz.
But the main reason I bought this particular compass is because it has a built-in clinometer, which is pretty hard to find feature on lightweight handheld compasses.
Clinometers are very helpful in avalanche prediction because they let you measure the pitch of a slope in degrees. The most dangerous, slab avalanches occur on 25-45 degree angle slopes, but with careful terrain selection and a clinometer like this, you can avoid them. There’s also useful for computing travel time and determining effort levels in conjunction with a map.
However, figuring out how to use the clinometer on this compass was really frustrating. I couldn’t find any documentation about it from Brunton or anywhere else on the web. I did eventually figure it out on my own, but it seems like a pretty big oversight by the manufacturer. I even contacted them about it, but never got a response.
Directions for using the Brunton 15TDCL Clinometer
Zeroing the Clinometer
Open the compass and lay it on flat ground on its side. Turn the red bezel so that the North is pointing up, perpendicular to the base plate. Inside the compass housing, you’ll see a small red arrow on a triangular piece of plastic that swings independently from the needle. Below it, there is a separate scale ranging from “E decl 90” degrees to “W decl 90” degrees, and the little red arrow should be pointing at 0 degrees, halfway in between. This scale is used for measuring slope angle.
Measuring slope with a ski pole
If you have a ski or trekking pole, lay it on the ground, on a representative portion of the slope you’re trying to measure, with the basket facing straight downhill. Next, lay the open compass on the pole with the long end of the baseplate lying on the pole. Find the little red arrow and read of the slope angle.
Sighting a slope angle from above
If you’re standing on top of a big hill or mountain, you can “shoot” a slope angle from above. Sight a point at the base of the mountain, looking just over the top of the base plate at your target below. Have a buddy locate the red arrow on the compass, while you stand still, and read off the declination angle.
Sighting a slope angle from the side
If you think a slope might avalanche, you probably don’t want to shoot its angle from its base. You can however determine its slope from an adjacent hill but aligning the top of the baseplate with the profile of slope you want to measure. Same as before, have a buddy locate the red arrow on the compass, while you stand still and read off the declination angle.
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