Since the manual roughness counter displays the raw roughness counts, only the odometer sensor needs to be calibrated so that the distance and speeds are correctly recorded.

The MRC has on one side five dial pots with numbers from 0 to 9. These are used to set the calibration factor.

Before calibration you must measure a distance of at least 100 m. The longer the distance the lower the error will be. Clearly mark the start and end points with chalk or paint on the road.

To set the MRC to calibration mode adjust the dials so that they are reading 01000 from left to right. In this state every time the system receives an odometer pulse it is displayed as a distance of 1 m. The figure below shows the setting of the dials for calibration.

• Drive the vehicle so that the tyre is over the start mark.
• Mark on the tyre the location of the paint mark.
• Turn on the MRC.Drive the vehicle to end mark.
• Drive the vehicle so that the mark on the tyre is on the ground past the end mark.
• Measure the distance from the end mark to the point where the tyre mark is on the ground. Add this to the distance between the marks to get the total distance travelled.
• Record the number of pulses on the Total Distance display.

The calibration factor is calculated as:

Factor = (Pulses received x 1000)/(Actual distance travelled in metres)

The five dials should then be turned so that they read this calibration factor. For example, if 265 pulses were received over 100 m the display would read 265. The calibration factor would then be:

Factor = 265 x 1000/100 = 2650

The dials would be set to 02650 as illustrated below.

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