Goniometry or electro-goniometry are the easiest measuring methods but depending on the assessor of varying degrees of accuracy and reliability. The literature tells us an experienced physio should be with 5 degrees of accuracy if it is intratester this will obviously go down if it is inter-tester. Electro-goneometry is about 3 degrees but requires a lot more time and effort to get it right.
More accurate is radiography but it is difficult to get past Ethics these days because of the radiation.
Without teaching you to suck eggs if you can standardise the start and finish positions hand held goniometry might be the way to go. In addition it is a clinically relevant tool.
If you wish to discuss more email me at: [email protected]
Hope it goes ok.
Alan Esnouf.