If you use a Bahtinov mask you will know that to achieve focus you need to get the middle spikes exactly centered between between the two sets of outer spikes. This can be difficult to judge by eye alone. This little program provides a resizable guide that you can position over an on-screen Bahtinov display. Once you have centered the guide over the middle spikes and rotated it into alignment you can immediately see if the two sets of outer spikes fall over or between the same tick marks either side of the guide's central line.
The small Control Panel is used to move, rotate, resize and adjust the colours of the guide.
In this example the tick marks at the outer edges of the guide show that the two sets of outer spikes are evenly spaced either side of the middle spikes.