Neil,
Measuring the frame angles is just a starting point based on the idea that the top tube will sit parallel to the ground (on a frame without a sloping top tube).
The important thing about frame angles is how they will affect the ride and handling of the bike. The fork rake (or trail) is also an important factor.
The measurements need to be taken with a set of same size wheels in place and the bike standing upright with the fork straight ahead.
I've been using an inexpensive plastic dial protractor with a magnetic base to make these measurements for years. I also have a more expensive digital protractor but they give about the same results.
Here's a link that shows a lot of different types:
http://www.thefind.com/
The only problem with these protractors is on small framed bikes with short head tubes and sometimes frames with a head tube badge. It those cases you can sometimes measure them from behind the head tube with some accurately ground square steel bits as spacers between the tube and magnetic base.
Chas. Colerich Oakland, CA USA
Neil Foddering wrote:
> I have tried, without success, to measure the frame angles on my 1930s and 40's bikes; does anyone know whether a purpose-made tool is available to do this (preferably idiot-proof)?
>
> Neil Foddering
> Weymouth, Dorset, England