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Application Note


Detailed Instructions for Using the Auto-Scale Factor

Although the Scalex PlanWheel has a number of built-in scale factors, it can also be used when the scale factor is not shown on the drawing or may be incorrect. This feature is called the "auto-scale" and is represented on the display by a wheel symbol. The auto-scale is useful for plans which may have been reduced or enlarged, or on maps.

To use the auto-scale, at least one distance must be identified on the print. For blueprints, use the largest distance which is indicated anywhere on the print. On a map, use the bar which shows distance or mileage. It is usually located toward one edge of the map. For the greatest accuracy, roll the entire length of the bar.

The procedure for setting the auto-scale is simple after you do it once or twice. Follow these detailed step-by-step instructions until you get the hang of it. (If you get stuck, start over at number 1)

1. Press CLEAR.

2. If you are not already reading in the units you want (MI, FT, KM, etc.), press UNITS until you get to the proper units. (Note - If you cannot find the correct units, see note 5 below)

3. If you are not already on the auto-scale (wheel symbol), press SCALE repeatedly until the wheel symbol shows. (Do not hold the button down, just press it and release it - repeat until you get to the flashing wheel symbol.)

4. Once you have the wheel symbol (flashing or not), press and hold SCALE for two seconds. If you have done everything correctly to this point, you will see a row of seven zeroes across the top of the display with the left-most zero flashing.

5. Carefully roll the wheel over the known distance.

6. Enter the distance you rolled onto the display. Do this by using the blue left and right arrows to move the flashing digit (left arrow = ADDER and right arrow = SCALE) and by using the blue up and down arrows to increase or decrease the digit (up arrow = SQ/CU and down arrow = SENSE).

Example: To enter 180 (starting with all zeroes, the left one flashing), press:
Right arrow (SCALE) - moves the flashing to the second digit (hundreds).
Up Arrow (SQ/CU) - sets the distance to 100.
Right arrow (SCALE) - moves the flashing to the third digit (tens).
Down arrow (SENSE) twice - sets the distance to 180.

7. When the distance is correct, press the blue circle (UNITS). The auto-scale should now be set correctly. Verify this by rolling over the known distance again and checking to see that you get the correct result.


1. You may roll the known distance and enter the corresponding number in either order.

2. The auto-scale will stay set even if you go to a different scale factor, then come back to the wheel symbol. It will also stay set if the scaler turns off. (If you change the batteries, however, the auto-scale will be lost).

3. The actual scale factor will not be displayed. Only the wheel symbol is displayed. If you wish to see the actual scale factor, you may roll the scaler a real distance of one meter and read the length in meters on the PlanWheel's display. (Or you may roll the scaler a real distance of one foot and read the length in feet.) Notice that the scale factor may include a decimal fraction.

Example: If you roll a real distance of 10 cm and enter the distance as 20 m, the scale factor will be calculated inside the scaler as 20 / 0.10 = 200. Then, if you roll the scaler over a distance of one meter, the length will display as (approximately) 200 m, indicating a scale factor of 1:200.

4. If, when you are entering the auto-scale, you realize that you have made a mistake, push the CLEAR key to cancel. This will return the PlanWheel to normal operation. Whatever scale was in the auto-scale previously will still be valid. Then you may start over.

5. The PlanWheel can be set to read in U.S. standard units (MI, YDS, FT, IN) only, or in metric units (CM, M, and KM) only, or in both U.S. standard and metric units. When selecting the units of readout before setting the auto-scale, if you cannot find the correct units, do the following: Hold down CLEAR and, at the same time, press UNITS. Repeat until you find the correct set of units. Then let up CLEAR. (For more information, refer to the instructions that came with the PlanWheel.)

6. If you are measuring from a nautical map, you can use statute miles (MI) instead of nautical miles. Since you enter the known distance in nautical miles, it will read back in nautical miles. (However, if you switch to another readout, such as yards, the conversion will not be correct.