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OverviewBearings 1
It helps if you have a demo silva style compass to use for this. You can make one out of a clipboard, a photocopy of a 0-360 protractor with an arrow, and a chunk of red coreplast, painted black or white at one end for the needle.
If you want a long rubber band chain can be use for magnetic force to attach to one end of the needle.
At this point you show them with the model how to set a bearing, then hold the compass and rotate their body so that they are facing the bearing.
This can be followed with a quick game of "Simon Says" As you repeat bearings, you will find that some kids remember where they faced last time, and will turn first, then set the compass. This is good. They are developing some intuition here. But make sure they set the compass and check.
This one can be done indoors.
Now go out to your Upper Fields again.
If you don't have a football pitch, mark out 100 meters.
Teach them what a pace is. Have them walk the 100 meters, and write down the number. Have them walk back, and write down the number. Repeat there and back once again.
With senior boys, many of them will have a 2 meter pace. They tend to overstep when pacing. You don't care. They won't be counting kilometers.
Now ahead of time you have to have carefully recorded GPS locations for your 22 signs. Ideally you have done this several times, thrown out the junk and averaged the rest so you know where each sign is to within 5 meters.
Plot thsie on OziExplorer.
Using OziExplorer or a spreadsheet and trigonometry, figure out the bearings between tags.
Each kid gets a sheet that looks like:
Go to Tag C. From C set a bearing of 220. Walk until you run into a tag,
counting your paces. Record the tag, and the number of paces.
It's ok to miss the tag. When you actually see, it change your course to reach it.
From this tag, set a bearing of 95. Walk until you run into a tag, counting your paces.
Each route comes back to you in 3-4 steps.
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Have 4-6 starting tags, but generate enough routes so that you have more routes than you do students. It will throw them for a loop when they go with another student from C to Q, then diverge in different directions from Q.
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As they come in look at their numbers. Since their pace isn't calibrated, the absolute numbers will wander a bit, but the long legs should be longer than the short legs. Point out with statemetns like this; "Isn't Q to S a lot longer than Q to C?"
When they all have gotten back, point out some of the discrepencies that you saw, and ask why they occured. Reasons that could come up:
- Miscount. Repeating a decade, dropping a hundred.
- Bad bearing, resulting in two sides of a triangle. Good for up to 20-30% too big.
- Not doing it and making up a number.
Discuss how to prevent these errors.
Now have a mini rogaine. Break them up into pairs, putting the best with the worst, second best, with second worst.
Each pair gets a sheet with 3 letter tags on it. From each letter tag tehre are 3 controls, each with a bearing and range. Two of them are fairly short -- 20 to 40 paces. The third is longer or in tougher terrain.
Working as a pair they try to find the 9 controls.
You can reuse the tags, but not in the same order.
Thus team one gets tags A C Q while team two gets tags C F S and team three gets tags B G C. Thus Tag C is first once, second once, and third once.
Make up your tag sets, and cut and paste to make up the sheets.
Give them 45 minutes to an hour to do the tag sets.
This is a good one to have before a break. During the break, talk to your good guys. Find out how the bad ones did. Check the middle guys. Count how many they found. What you are looking for are guys that are clueless. You may have to run them through again, doing a couple with them one-on-one.
This one is a fair amount of work to set up. If you have 12 students you need 4 tag sets. For each one, you need to measure the distance accurately -- within 2 meters. YOu need to have the bearing correct to within 2-4 degrees. (I have a sighting compass with a mirron and a tiny magnifying glass over the bearing marker. After much practice I can get a bearing right to within 2 degrees -- about two times out of three. I now make a point of measuring both the bearing and the back bearing. Check, double check. Check again.
A 100 meter tape, a sighting compass, and a runner to hold the tape help a lot.
You cannot do this with GPS, unless you have access to a differential GPS. GPS have an intrisic error of about 3 meters. On top of this, the short time error is another few meters. 5 meter accuracy is about as good as it gets, no mater what the GPS claims. A 5 meter error at both ends of a 30 meter run means that the distance could be as short as 20, as long as 40, and only about a 50% chance of it being between 27 and 33. Worse, the bearing could be off by as much as 20 degrees, and is likely off by at least 10.
The GPS error is pretty constant. As the distance increases, the error from the GPS becomes small compared to the other errors. So for 100 meter distances, the GPS error is likely as good as you can do with compass and pace.