Rear Glass Reveal
Dec/090
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How do you use a Suunto Instrument (Finland) Type: PM-5/PC 66? It is an instrument for estimating tree height.
This is a product used by forestry industry to estimate tree height. It is hand held and smaller than a pack of cigarettes. The case is brushed metal with a glass lens that reveals a balance wheel that has 2 ninety degree sectors on the weighted bottom half. It has a sight lens in the bottom that reveals % of angle and another number. It also has a conversion chart on the back that converts % to some symbol that looks like a lower case "a" with rear facing tails at the top and bottom. There is a red dot on the very top of the instrument. The face of the balance wheel has "Left PC (%)" above the left 90 degree sector and Right 1:66 above the right 90 degree sector.
Yeah, it's true. A clino does have a degree scale visible when viewing a tree. But I always used the percentage scale because it is easier to calculate in the field. Okay, listen up because although it's an easy instrument to use you will get more accurate readings if you use it properly.
You will need a clino, a 30m (at least) tape measure, writing materials, a tree, an assistant will make the job easier.
1- Visualy determine the highest point of the tree. Why? because not all trees are straight like pine trees. You will need to do this ready for step 2.
2- Your assistant will stand directly below this highest point and hold the tape at zero. This point will not always be beside the tree trunk. Depends on the lean / shape of the tree.
3- Depending on tree height walk back with the tape measure until you can comfortably see the tree heighest point. Comfortably means without straining your neck, okay? Do it for weeks and you'll know why.
4- View the tree thru the clino with BOTH eyes open. One to see the tree and the other to read the % scale on the clino.
5- Read the clino percent scale at the top of the tree. Also note if its + or -
6- Now this is important so listen up. Now view the base of your assistant. If he is beside the tree you can use the tree instead.
7- Read the percent scale. Note + or - again. Write both answers down so you dont forget.
8- If both answers are from the same end of the scale eg + then subtract them. If one + and one - then you add them together.
9- The tree height is then determined thus. The answer from the numbers you wrote down (maybe 50) will be the percentage of the distance you are from the tree (%50).
Example: you are 20 meters / yards from the tree. Your top reading was + %40 your base reading was -%10 because you have both + and - you will add them = %50 so....%50 of 20 = 10
Your tree is 10 meters / yards tall.
A couple of tips for you:
If for some reason you can't see the tree base use your assistants eyes / head / helmet for the base reading. This may cause both readings to be from the same end of the scale so remember to subtract them if so. At the end of your calculations just add the height of your assistant for the answer. This is called "pole height"
Another different way is to walk towards the tree viewing the tree top thru the clino. When the tree top gets to either %100 or 45 degrees you are one tree height away from the tree. Just measure the ground and add on your own height up to your eyes.
Sorry its a long answer, I tried to keep it simple for you.
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