When I bought my splits machine, I had no way to easily calculate the angle of the machine. So I dialed in a visual 90° angle and started looking for convenient ways to measure the machine’s leg length. I measured a leg length of 28 to the screws at the end of the leg, and then measured the “base” of the triangle between the opposite leg’s screws. I discovered a measurement of 39.5, which gave 89.717°. Measuring from the absolute ends of the machine legs show a leg length of 29 and a base (spread distance) of 41, for a result of 89.996°. This was very accurate and since it was round numbers I was happy with the results.
I would then use an on-line triangle calculator to determine the angle of my splits for the session by measuring the distance between the legs.
Months later it occurred to me that I could just measure the distance between the legs and use that to index a previously calculated figure. So I re-measured 180cm from end to end at 180°, and then 125cm end to end for 90°. The implication being that the factor is about 1.6° per cm as you go from 125cm to 180cm. To test this I dialed in a visual 135° using the tiles on the floor and measured 164cm. This is an extra 39cm, and I expected only an additional 27cm. So the figure gets more accurate as you get closer to 180°. What would be better, likely then, is to do a table of expected results based on the leg length and not rely on a formula.
However while doing the table I kept coming back to highly accurate visual results indicating that a leg length of 29 (88cm) was very accurate between 90° to 180°. It became simply too convenient to use this number. Yet, when measuring at 180° we got 180cm, so perhaps using a leg length of 90cm would be a bit more accurate.
As it turned out, a leg length of 90cm provided greater than a very careful visual tuning of the angle. At 135° and 90°, observed error was attributable to human error. For example, I tried to make the machine 135° and measured a 165cm spread from pad-end to pad-end. This would give us 132.9°. But when I went to visually check the degree I found it to be slightly inside 135°. Meaning, closer to 132.9°. Thus the leg length of 90° was adopted and used to key spread lengths to spit angles.
Table 1: Spread Length to Angle
| Spread Length | Expected Angle |
|---|---|
| 180cm | 180° |
| 175cm | 153° |
| 170cm | 142° |
| 165cm | 133° |
| 160cm | 125° |
| 155cm | 119° |
| 150cm | 113° |
| 145cm | 107° |
| 140cm | 102° |
| 135cm | 97° |
| 130cm | 92° |
| 125cm | 88° |
Table 2: Required Spread Length for Angle
| Angle | Spread Length |
|---|---|
| 180cm | 180cm |
| 170° | 179cm |
| 160° | 177cm |
| 150° | 174cm |
| 140° | 169cm |
| 130° | 163cm |
| 120° | 156cm |
| 110° | 147cm |
| 100° | 138cm |
| 90° | 127cm |
More later.