Special Telemeters and Custom Nomographs
Tutorials and setup instructions for specialist or custom-made Telemeters.
Wndsn Telemeter Recon Dog Tag
The Wndsn Telemeter Recon Dog Tag (Recon DT) is a companion piece for quick and also inconspicuous navigation and rangefinding with an angular scale and a multiplier scale.
The Recon DT is a mini Telemeter used to measure and calculate distance. Compared to the Quadrant Telemeter^{[1]} the Recon DT has a simplified angular scale at a lower resolution of 0.2° or 12 arcminutes.
Use the Recon DT for fast sightings: Find an object of known size at the distance you need to measure and determine its angular size or calculate its distance.
Inspired by both the medieval Kamal, a celestial navigation tool that greatly facilitated latitude sailing, and an ancient Viking navigation necklace pendant, the Recon DT fixates the distance to the measuring scale by way of creating a necklace that is holding the scales at a set distance, thus enabling accurate measurements.
The scales on the Recon DT are calculated in a way that enables the user to measure one-handed, no further setup required other than wearing the Recon DT around their neck.
How to set it up
- To install, loop the string through the hole at the top
- Find the eye-to-scale distance in cm on your instrument, e.g.:
o-25-(o
- Measure that exact length from eye to scale
- Fixate that same length with the string around your neck
Operation
- Keep the string taut, for exactly the distance set up from eye to scale
- Align the instrument‘s baseline to the top of the object to be measured
- On the α scale, read the angular size at the lower bound of the object
- To calculate the distance to the object: divide 57.3 by the measured angular size
- Alternatively, use the multiplier scale on the opposite edge of the Dog Tag
- Read the multiplication factor at the lower bound of the object
- Multiply the value with the known height of the object.
Accuracy
Accuracy is determined by two elements, provided that the string length is respected:
- The reading of the scale and approximation of the corresponding mark
- The estimation of the height of the measured object
For training and reference purposes, you may want to create a table of the exact height of common objects.
FAQ
Q: How do I use the multiplier scale?
The multiplier scale on the opposite side of the degree scale is where one-step operation becomes possible:
If the dimension of the sighted object is known, the marks on the multiplier scale give direct values to multiply with.
Note that you can measure in any unit (cm, in, ft) or system (metric, imperial, custom), the factors are always the same and return your distance in the same unit you used to approximate the object size.
If you know that the object in question is 4 m tall, and the multiplier scale shows a 15, you can calculate the distance as 4 x 15 = 60 m. If the object is 9 ft tall, and you get a 20 on the multiplier scale, the distance is 9 x 20 = 180 ft. Note the use of different units.
Q: How do I use the degree scale?
The degree scale measures the angular size^{[2]} of the object observed, in other words the measured height in degrees, (easily converted to multiplication factors as per the instructions on the instrument) which can be used when the actual height of the object is unknown.
1° = x 57 2° = x57 /2 = x 28.5 3° = x57 /3 = x 19 4° = x57 /4 = x 14.25 5° = x57 /5 = x 11.4 6° = x57 /6 = x 9.5 7° = x57 /7 = x 8.1 8° = x57 /8 = x 7.1 9° = x57 /9 = x 6.3 10° = x57/10 = x 5.7 11° = x57/11 = x 5.2 12° = x57/12 = x 4.75 13° = x57/12 = x 4.4
Q: Can I measure the width instead of the height of an object?
You can measure any dimension; width, height, etc., as long as it's on a plane that is perpendicular to you, the trigonometry doesn't care where in space the triangle is located.
Q: What about a scale graded in MIL?
The Recon Dog Tag is an instrument for hasty measurements with a resolution of 0.2° which translates to about 3.55 MIL. We make a 2 MIL resolution Recon Dog Tag upon request. If you need a finer 1 MIL precision, the larger sized NATO-MIL Telemeter provides a 150 MIL scale at a resolution of 1 MIL.
Note that the multiplier scale on the Recon Dog Tag provides a simple way to acquire MIL values (conversely, the MIL scale on other Telemeters provides multiplier values). The angular size of an object in MIL is the reciprocal of its multiplier and vice versa.
MIL = 1 / Multiplier x 1000
Multiplier = 1 / MIL x 1000
See also:
References:
- Recon Dog Tag Vs Telemeter ↩
- Wndsn: Angular Size is an angular measurement describing how large an object appears from a given point of view. Angular size is a relative term that does not say anything about the actual size of the object which is observed. ↩