Here's a few computer tips:

First, hold down Alt and hit 248 on the numpad: °_°

And when it comes to measuring stuff from pictures, I like to use Paint Shop Pro (pretty sure Photoshop is similar enough). The geometric distortion tools can be pretty handy...

Say all you have is a photo of a photo, and it's not even straight-on, you can use perspective correction to fix it, and/or if the shot itself is off-centre, you can correct a little bit for that too. There are also tools to correct for lens distortion as well.

But the main utility for this sort of stuff comes into play when you resize the pic so one pixel is 1mm (imperial be damned). First, jump on Google's image search to make sure you're you're starting with the largest copy you can find (hit the little camera icon to paste an image's address or upload one). In this case, no dice. So I had to resize the pic 435.5% to get there, and it's a bit fuzzy, but just good enough to be sure you're making reasonably accurate measurements. (Neatly enough, at this scale a bike nearly fills HD resolution, and my telly is my monitor.)



Now I can just use the straighten tool to find angles and/or rotate the pic to use the selection box to measure anything.