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.

Measuring Slope (Grade)

The grade (also called slope, incline, gradient, mainfall, pitch or rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. Grade is a special case of the slope, where zero indicates horizontality. A larger number indicates higher or steeper degree of tilt. Often slope is calculated as a ratio of "rise" to "run," or as a fraction (rise over run) in which "run" is the horizontal distance and "rise" is the vertical distance.

Elements in slope calculation.

Elements in slope calculation.

To measure slope, we have various options on our quadrant. They all start with aligning one of the edges of the device with the slope to be measured. To read the result, we can choose between 4 scales:

  1. The degree scale on the quadrant
  2. The degree scale on the edge of the device
  3. The percent scale on the quadrant
  4. The shadow square

Measuring in degrees

Degrees measure the angle of inclination to the horizontal. This is the angle θ opposite the "rise" side of a triangle with a right angle between vertical rise and horizontal run. The tangent of θ is equal to the rise divided by the run. Therefore, the inverse-tangent of the rise divided by the run will give the angle:

tan(θ) = rise / run    
    θ  = arctan(rise / run)

Measuring as percentage

Percentage, is the result of the formula:

100 × rise / run

which could also be expressed as:

100 × tan(angle of inclination)

Measuring as ratio

Gradient, or ratio of one part rise to so many parts run. For example, a slope that has a rise of 5 feet for every 100 feet of run would have a slope ratio of 1:20, read as "one in twenty slope".

Combining the use of shadow square and slope scale, we can nicely visualize rise and run and read its percentage in one step.

To calculate the degree of slope from a rise/run pair, we set the values of rise and run on the shadow square and directly read slope percentage and angle on the respective scales.

Of course, if we have a given slope value in percent, we can convert to degrees and vice versa, by using the two adjacent scales.


Measuring slope in degrees

Measuring slope in degrees: 19° on the transversal scale, measured parallel to the short edge of the Telemeter. Note the quadrant scale showing 90 - 19°.

Measuring slope in percent

Measuring slope in percent, parallel to the long edge of the Telemeter: ~3° or 5%. Also note the value on the shadow square: between 0 and 1 on the 10-scale, thus 1/20 (= 5%).

Let rise = 1 m, run = 20 m.


tan (θ) = (1/20)    
     θ  = arctan(1/20)    
     θ  = 2.86°


Slope = 1/20
      = 0.05 × 100
      = 5%


Slope = 1/20
      = 1:20

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