Now look at the number 15 on the disk. Between 15 and 16 each calibration mark is equal to .2 and would be read as 15.2, 15.4, etc. If you were solving a problem with an airspeed of 150 knots, the first calibration past 15 (150 in this case) would be 152. The spacing changes again at the number 30, where each calibration becomes .5, and at 60, where each calibration equals 1. Before you read a value from the disks, be sure you understand what each line of calibration is equal to.
You will use the slide rule side to establish ratios. With the numbers matched, the ratio is 1 to
1.Now set the number 60 (the rate arrow) directly opposite to (or,
Look at the inside scale on the disk, where the lines of calibration look like clock times: 9:00, 6:00, etc.— these express hours. The inner scale is in hours and the middle scale is in minutes. 1:10 is directly below 70; one hour and ten minutes is the same as seventy minutes. 5:00 is printed below 300 minutes, and five hours is the same as 300 minutes. To convert minutes to seconds, place the rate arrow opposite to the minutes on the outer scale and read seconds opposite to the “seconds” arrow, just to the right of 35 on the inner scale.
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