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DATE: 2018-02-21
AUTHOR: John L. Godlee
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I've just come back from fieldwork in Angola, during which I had to measure the diameter at breast height (DBH, 1.3 m) of the trunks of about 2300 trees. To estimate the diameter I used a DBH tape, which is a type of tape measure similar to that which you would find in a tailors, made of frabric or fibreglass. The difference is that a DBH tape has two scales, the first is a normal mm scale, but the second is a scale which estimates the diameter of the tree trunk by assuming the trunk is a perfect cylinder and converting the circumference (C) using the formula:
DBH = \frac{C}{\pi}
There are plenty of resources on best practices for estimating DBH using a DBH tape, how to deal with irregular stems etc., the focus of this post is instead to show how to properly store a DBH tape to minimise tangling and to keep it compact while in a backpack.
The first thing to do is to roll up the DBH tape starting from the end with no metal hook, until you have about 20 cm of free end.
Next, pass part of the free end through the hook and pull it through.
Then, twist the roll so it sits inside the newly formed loop that was pulled through the metal hook. At this point the tape measure looks fairly compact, but the tape will be twisted.
Remove the twist in the tape by turning the hook end and make sure all parts of the tape are in aligment.
Finally, tighten the hook end around the roll of tape by turning the hook around the roll to take up the slack
Like this, the tape should stay together in a rucksack or pocket, allowing it to be quickly unrolled to take a measurement, without risk of it tangling round whatever else is stored next to it in the bag.
