Grid Protractor Question

[DayTrip]

While looking for another compass recently I stumbled upon a product called a grid protractor. I guess they are small clear plastic cards with measuring lines, etc to make plotting bearings, measuring distance and so forth easier and more accurate. Does anybody here use these products? They make it sound like a common item in the military, special forces, etc so I assume they have some value as a navigational tool (or they have successfully hooked me with their marketing hype ).

I guess my big question with their use is that they are preprinted in various scales. I do most of my bearing markings, etc on CalTopo maps. Is there a setting on CalTopo that you can make the map render to a specific resolution so that it corresponds to one of the grids on the protractor? Obviously you can zoom in and out on CalTopo to print the exact area you want so I suspect this makes a product like this useless. Wasn't sure if there was some way of you could set a ratio so they could be utilized in some way on CalTopo maps.

Any feedback on the topic would be appreciated.

 

[nartreb]

The size of your printouts is mostly up to your printer. Adjust your printer so that the scale on your printouts (for a given zoom level in Caltopo) matches one of the scales pre-printed on your compass/protractor.

Most backpackers' compasses have a ruler or two built into the side(s). It's only marginally useful to me, as I'm rarely travelling in a straight line anyway. I'm not usually navigating with great precision; if I want to measure distances on my map, I usually compare my thumbnail or some such to the map scale, then step that over my route. If I want a more precise distance I'll use the ruler on my compass, but I can't remember the last time I bothered. For trail distances, I'll usually mark my map in advance so I don't need to measure in mid-hike.

In Alaska, I have used my compass as a protractor for sighting angles to distant peaks to triangulate my location on a large map. That's not a terribly useful technique in New England, where if you've got good lines of sight, you probably already know where you are.


(I've been hiking in NH for a couple of decades, still haven't finished the Grid. It's been very protracted.
Children: the Grid Protractor.)

 

[Nessmuk]

I co-instruct a 2-day Land Navigation course for Homeland Security, mostly to law enforcement and SAR type students. The course was originally developed before I got there by army veterans, so the army navigation field manual and using the square plotting protractor play a big part in the lessons and exercises. The square plotter is used for reading and plotting UTM coordinates as well as a protractor. You can get them in different versions, depending on the standard scale of the map you have. As nartreb says, if you print your own map, you have to ensure it is printed at a standard scale set for the plotter you have if you want to use the coordinate measurement function. When we print small maps for desktop training, we have to adjust the printer scale by as much as 4% up or down depending on which office printer we use for them to match scale with the square plotter. But use as a simple protractor alone (not as a coordinate plotter) does not depend on map scale.

But a good baseplate compass is certainly an accurate protractor, and it also "remembers" the azimuth it is set to. I'm trying to lean the course away from having to purchase and bring that separate piece of specialized plotter equipment with you in the field. There are other very accurate methods to plot or measure coordinates without the specialized square plotter. The scale on the compass baseplate will do. Even a cheap (almost free) short metric scale ruler can be used on any random scale map, with just as much accuracy as the specialized square plotter/protractor. There's a neat trick for doing that, which is very easy but may not be obvious at first.

Most navigation should be done by pre-planning and terrain association anyway, with assistance from a compass. All you really need to navigate in most all regions in this area that we travel is a compass, a topo map, and ability to interpret the many constant navigational clues you see around you.

 

[peakbagger]

For land navigation, you don't need that much accuracy. There are so many introduced sources of errors elsewhere that its not worth buying a rarely used specialized tool. If you want to buy a toy to improve your accuracy a sighting compass is the way to go http://www.suunto.com/en-us/Product...&utm_term=1101012387678&utm_content=Compasses. I use one when trying to retrace the boundaries on my AT section. Just look through the lens at the correct magnetic bearing and then pick a spot far off in the distance that you can locate then let it go and find the easiest route to the that point, then repeat. I do count paces but it mostly by habit as bushwhacking up over cliffs and slabbing slopes introduces a lot of vertical angle error that screws up the distance. The standard warning about vertical angle correction is unless you are in the middle of a corn field, your measured walking distance is always going to be less than your map distance as the map distance is inherently horizontal.

One caveat on specialized compasses is that not all have a 360 degree dial, some have specialized systems so be careful when you order one

The vast majority of off trail travel is use the compass to get to a terrain feature from a known point and once at the terrain feature pick a new bearing. Distance is mostly used to estimate time to travel and that can really vary depending on conditions. An altimeter watch was the high tech tool when I started bushwhacking but they have basically been replaced by GPS units.

 

[egilbe]

Military uses for a protractor....well, let's just say that it's critical that they know their location within a few meters. Civilians only really need to know what side of which mountain they are on. Civilians have no need to call air strikes or artillery fire.

 

[DayTrip]

Thanks for the info. I had never seen one of these before so I was curious of it's use. They're certainly cheap enough that I figured if there was some benefit I wasn't aware of that made it worth the $5-$10 I'd pick one up. I'll keep doing what I'm doing now.

 

[Stan]

A couple thoughts on land navigation. For those who triangulate, be aware that iron in the environment can throw the compass off. I observed this once on North Brother trying to make sense of my compass bearings to identifiable peaks ... could have led to an error had I relied on it for a bearing to Fort.

The protractor could be an antidote for cabin fever for those of us with a fondness for maps and navigation. As a practical matter, not necesary for hiking, even to trailless destinations.

My favorite compass is a WW II hand-me-down from my father. It is in an army green canvas pouch attached to my shoulder strap. He was in an anit-aircraft batallion. The hairline sighting, magnifier and precision were useful, I presume, for stationary targets. Overkill for most of my needs but close to my heart anyway.

 

[nartreb]

Yes, it's best to use at least two distant landmarks for triangulation, rather than merely one landmark plus magnetic north. This protects you against both local magnetic effects and regional/temporal changes in magnetic declination.

 

[John H Swanson]

I used to be in SAR and wanted to make some plotting tools before I bought a compass that had them built in. There was a website called something like map tools. They sell similar tools. You might find something interesting there.

Eventually I chose to download an image and print my own on transparency paper. Had to punch a small hole for the pen to touch the paper.

With regards to your question. I use my compass as a protractor.

 

[DayTrip]

I used to be in SAR and wanted to make some plotting tools before I bought a compass that had them built in. There was a website called something like map tools. They sell similar tools. You might find something interesting there.

Eventually I chose to download an image and print my own on transparency paper. Had to punch a small hole for the pen to touch the paper.

With regards to your question. I use my compass as a protractor.

Map Tools was the site I was linked to. The transparency paper is a good idea too.