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Wndsn Quadrant Telemeters

Wndsn Graphical Telemetry Computers: Low tech, high utility distance and altitude nomographs from the Wndsn applied science lab

Wndsn Quadrant Telemeter Tutorials

Making the most out of our graphical telemetry computers.

Like with many complex instruments, there are multiple ways to solve certain problems and to measure the required inputs. Combining the various functions leads to a multitude of advanced uses. See also the printed manual.

Using the Telemeter as Coordinate Scale

Level: Intermediate

How to measure distances on a map with the Telemeter.

The majority of our Telemeters feature an angular scale (those that show 180/π or 57 as eye-to-scale distance) that doubles as a metric ruler, where 1° = 1 cm. A handy application of a metric scale is that of a coordinate scale to measure or transfer right-angled coordinates from or to topographical maps with UTM, MGRS, USNG or other metric coordinate systems.

Most maps are in 1:25,000, 1:50,000, or 1:100,000 and 1:250,000 scale. On our metric Telemeter, on the angular scale, 5° ≙ 5 cm.

Hence:

  • at 1:100,000, 5 cm = 5 km and 0.1 cm ≙ 0.1 km
  • at 1: 50,000, 5 cm = 2.5 km and 0.1 cm ≙ 0.05 km
  • at 1: 25,000, 5 cm = 1.25 km and 0.1 cm ≙ 0.025 km
  • at 1: 250,000, 5 cm = 12.5 km and 0.1 cm ≙ 0.25 km

... as well as multiples/fractions of these, by multiplying or dividing the respective scale by 10.

We can derive a simple rule here, namely that:

  • at 1:100,000, we use the measured value as is
  • at 1:50,000, we divide the measured value by 2
  • at 1:25,000, we divide the measured value by 4
  • at 1:250,000, we multiply the measured value by 2.5

To determine a position, check the scale of the map, then read the Easting (right) value, and then the Northing (up) value.

Example

We have a 1:25,000 topo map, here is how to get the Easting and Northing values.

Using the Telemeter as Coordinate Scale.

Using the Telemeter as Coordinate Scale. Getting the Easting value.

Using the Telemeter as Coordinate Scale.

Using the Telemeter as Coordinate Scale. Getting the Northing value.

Easting

To get the Easting value, position the Telemeter horizontally on the map with the 0 of the angular scale aligned at the next (left) grid line. Read the value where the scale touches the target.

We have a reading of 3.4 cm, which at 1:25,000 means:

3.4 × 0.025 = 0.85    
or even easier:    
3.4 / 4     = 0.85

For an Easting value of 0.85 km or 850 m.

Northing

To get the Northing value, position the Telemeter vertically on the map with the 0 of the angular scale aligned at the next (lower) grid line. Read the value where the scale touches the target.

We have a reading of 0.5 cm, which at 1:25,000 means:

0.5 × 0.025 = 0.125    
or even easier:    
0.5 / 4     = 0.125

For a Northing value of 0.125 km or 125 m.

The Position

The last step is to combine the two values with the base values of our grid:

 422.000 E + 850 m    
5022.000 N + 125 m

For a resulting position of:

422.850 E 5022.125 N

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