SMoffat - You can use Pixelstix for both horizontal and angle calculation. Sorry I should have mentioned this sooner is another good 'horizontal' calculation program is Go Horizontal. Its costs less than $5 too and is even more simple to use.
I would go with Go Horizontal for the 180, and then ImageJ for the angle calculation. Pixelstix combines both but is more complicated to use.
I would go with Go Horizontal for the 180, and then ImageJ for the angle calculation. Pixelstix combines both but is more complicated to use.