Archery Sight Mark Calculator
This free calculator allows you to estimate all your archery sight marks (indoor, outdoor, metric and imperial) given just three measured values (and your arrow draw-length). You can manage sight marks for different archers - or for different bow set-ups - and you can save the secure data to your local device (phone, pad or PC) so that it can be used off-line.
Sight marks are entered as pairs of numbers. The first number of each pair is the length of the sight-arm extension, which is the distance from the centre of the sight pin to the back of the bow; measured in standard units, such as inches or millimetres. The second number is the position of the pin along the sight scale. It may be specified in standard units or, because some sights use custom scales, it may be given in sight-specific units (e.g. Shibuya or Cartel) selected from a drop-down menu.
The estimation process involves fitting measured sight marks to a mathematical curve and not a straight line like most other sight-mark calculators! The non-linear fit means that predicted sight marks are accurate at both very long and very short ranges. The form of the curve is derived from the equations of motion for an arrow, and the fitting is done using a least-squares method called the Levenberg-Marquardt algorithm. A minimum of three sight marks for three different ranges are needed. Any fewer and the algorithm cannot produce an answer. With precisely three measurements, the fitted curve should pass through all the measured points exactly. With more points there may be small differences - perhaps you need to fine-tune your measurements?
Remember, all estimates are only as good as the input data. And don't expect to get accurate results for one hundred yards using just your indoor sight marks! For best results, use measured sight marks over a wide spread of ranges.