This vintage THS Planimeter 55-8407 is complete and includes the original hard case. Planimeters are used to measure areas on maps, plans, blueprints or any scale drawing or plan by surveyors, foresters, geologists, geographers, engineers and architects. They consist of a tracer arm having tracing point and a carriage with a measuring wheel, counter dial, sliding roller, pole weight, pole arm and magnifying lens. Free Shipping within the USA. Scroll down for info on how to use a planimeter and detailed condition.
CONDITION/MARKINGS - The set is complete and appears in good working order (moving parts all function well). There is some light-medium corrosion on the metal parts but nothing too bad. The magnifying glass has a light scratch on the bottom portion. The hard metal and vinyl case is in good condition, opens and closes easily. No dents or damage. Missing the liner on the inside lid. The latch has very light corrosion and reads - Yokoya Tokyo with an image of a dog's head. The tracer arm is marked Constant 27293, Made in Japan, 1:1 .01 sq in, no 15121. The encased counter dial reads THS Charvoz, Cat.No. 55-8407, zero set device. Case measures 9 x 4 1/2 x 2 in.
Using a Planimeter
To use a mechanical planimeter, a "constant" is first determined by choosing the shortest possible arm length which will cover the area to measure, and tracing the boundary of a known area (a 2 x 3 business card for example). Once the known area is traced, you can see how many revolutions the dial scale indicates. The known area divided by the dial reading equals the constant. Once the constant is determined, the measuring dial is reset and the boundary is traced by moving the magnifier over the boundary in a clockwise direction. The reading on the dial is multiplied by the constant to give the desired area of the plot. This constant can be used so long as the length of the pole arm is not changed.
Simplified Directions for Use: 1.Begin by drawing a precise known area. In my example, I used a standard business card of 2 inches x 3 inches for an area of 6 sq. inches. 2.Set the tracer arm for the shortest area which will trace the boundary you are working with. The shorter the arm, the more accurate the measurement. 3.Place the tracer in the approximate center of the area to be measured and adjust the angle of the pole arm to approximately 90 degrees. 4.Place the tracer on the area boundary at the starting point, reset the counter to zero, and trace the area in a clockwise direction. 5.Read the number of revolutions from the vernier and the dial. Divide the known area (6 in the business card example) by the reading on the vernier to get the constant. (Expressed as square inches per revolution) 6.Use the same procedure to trace the area on the map or drawing. 7.Convert square inches to actual area by using the scale of the map and multiplying. 8.The constant can be used for any number of measurements. If you change the tracer arm length, you must calculate a different constant.
MORE INFO FROM THE INTERNET - Mechanical (non-digital) planimeters feature a pole arm, tracer arm, tracer magnifier, recording dial, and vernier measuring wheel. Some models have adjustable length pole and tracer arms, while others are fixed length. All have a reset which returns the measuring dial and vernier scale to zero before the next use. Digital planimeters are computerized. They give a direct reading of the area traced as square inches or centimeters, with some reading directly in any unit of area including acres, square meters, square kilometers, etc. The most advanced units will also store data for downloading into a personal computer. Most digital planimeters have various memory functions which enable you to add areas, accumulate measurements and average multiple measurements. Digital planimeters are available with pole arms or rollers.