Hello and welcome to this lesson of the online course Wilderness Navigation Masters, where you will learn how to estimate how far away you are to a landmark.
You will learn:
Knowing that will help you :
- 1) To locate yourself in regards to a landmark.
Because, with a back bearing plotted on your map, you can be sure that you are along this back bearing line. But where on this line? this is when estimating distance gets useful.
- 2) The second scenario when estimating distance can help you, is to know how much time you need in order to arrive at a destination.
Yes, you can know that from your map, but why not learn these techniques that don’t require any tool like a map. It can happen that you lose your map, or you arrive at a place without it’s a map or simply you can’t locate yourself on your map.
Moreover, you can use it just to verify the results of other techniques like triangulation in order to locate yourself.
Now that you’ve started seeing the importance of measuring how far away you are to a landmark without the help of your topographic map, let’s start with the first technique.
Thumb and eyes technique:
Step 1: Hold your arm in front of you, with your thumb up.
Step 2: Close one eye, and align the edge of your thumb with the edge of your landmark like that.
The important thing here is to align the edge of your thumb with something that you know how he measures, you will know why in step 4.
Step 3: Without moving your thumb, switch eyes. Your thumb will appear to change position, but it’s not true.
Step 4: Estimate how much your thumb jumped sideways.
In order to know that, if you aligned your thumb with a car that is 4 meters long, and your thumb jumped half the car, your jump measure 2 meters.
Step 5: Multiply that number (2 meters in this case) by 10. And from that, you know that you are approximately far away from the car by 20 meters.
The second technique that I want you to know about, in order to use it to measure approximately how far away you are from a landmark, is pretty similar to what we’ve just seen.
I will call it the Mils technique because it’s based on milliradian (often called mil or mrad ) which is a measurement unit used for very small angles.
Do you remember when we were talking about the magnetic declination diagram, and I’ve said to you to not care for the Mils because it’s just an angle measurement unit used by the United State military, this is what I was talking about, it’s the milliradian.
In a 360° of a circle, there are 6400 mils.
This is why it’s more precise.
This will help us to measure how far away we are from a landmark because at a distance of 1 km, an angle of one mile corresponds to 1 meter.
So the formula is :
Distance (in km) = Dimension of the object in meters, subtracted by the angle in mils, under which we see the object.
For example, a house that is 10 meters high, seen with an angle of 5 mils is 10 substrated by 5 ( which equals 2 km) far away from us.
Like I’ve said before, in this lesson, we will not use any tool, we will stay with what we have with us most of the time. And in this case, we will use our hands again.
If you place your hand in the front of your eyes, elbow straight, your fingers cover approximately these angles.
Let’s say that I want to measure how far away I am from this house that measures approximately 10 meters.
- Step 1: aim at it with your hand to measure the angle.
In this case, it’s an angle of 30 mils
- Step 2: Apply this formula. And in this case, it’s 10 meters subtracted by 30 mils which equal 0.3 km, which equals 300 meters or around 1000 foot.
So, we are far away from this house by 1000 feet.
That’s all for this lesson, if you still have a question or you have another technique to estimate distances in the wilderness, you can share it with us in the comments section below.
Thank and see you in the next lesson.
Last modified: June 7, 2021