ITF

50 A surveyor's level can be checked using the standard 'two-peg' method: Place the level midway between two pegs at different heights 10 m apart and read the staff on each peg. Calculate the height difference between the pegs. Move the level 1 m past one of the pegs and read the staff on each peg and calculate the height difference again. The difference in the height differences is the collimation error in mm/10 m. Test procedure 1. Using the distance-measuring device, find the x- and y-coordinates of the corners of the TPA (B2, B6, H2 and H6 in Figure 4). Temporarily mark a 7.5 m grid on the court surface (e.g. using coins). The centre point of the grid will be at the midpoint of the net, and the perimeter of the grid encloses the PPA (C3, C5, G3 and G5 in Figure 4). 2. Using the surveyor's level, establish a horizontal reference plane using a fixed datum, e.g. by placing the level near the centre of the court. Measure the vertical distance between the surface and the horizontal reference plane at the four corners of the TPA and each of the 15 points of the PPA grid (19 points in total) using the measuring staff. 3. Repeat the measurements in reverse order. Check any measurement for which the discrepancy between the two values exceeds 1 mm. 4. Measure the evenness of the court at the 19 points (refer to method ITF CS 02/02). Calculation of results Slope 1. Calculate the height difference for each pair of points along the two sides of the PPA (C3 and C5; D3 and D5, etc., in Figure 4) and take the mean of these five values. 2. Divide the mean by the width of the PPA (i.e. 15.0 m) to give the side-to-side slope. 3. Repeat this method to determine the end-to-end slope (using the points along the ends of the PPA, divided by 30.0 m) and the two corner-to-corner diagonal slopes (using the corner points of the PPA). 4. The maximum of these four gradients is the test value for slope.

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