I've had that electronic test.. hurt like a bitch! Mind you, that's because my tendons were perfectly OK and it was a cartiledge I'd popped...
Have you considered using a pen and tablet mouse? It's what I use at home and it's made a great difference.
I would suggest asking someone to come and observe you as you work. A second point of view is often invaluable in these situations, if that person is a trained Workplace Risk Assessor, then all the better! Another person can tell you at what angle your arms and legs are in relation to the desk (legs and arms at right angles used to be the suggested preference but now they recommend that it is more, to avoid compressing the blood vessels in the upper thigh/hip and elbow). The other person will also be able to tell you how frequently you move, what you stretch for without realising, how you maybe hold something awkwardly and point out things you didn't even know you did.
Use footstools, monitor raising blocks (or the Yellow Pages) and adjust your chair occasionally to get the best seating arrangement. See if you can 'test drive' different tracking systems or mouse arrangements... there are many on the market and not all are suitable.
Stretch your arm out regularly - you should be taking a break from your screen 10 minutes out of every hour and never work more than 5-6 hours without a 30 min break away from your desk. There are several Pilates style exercises that you can do whilst sitting at your desk, that will encourage blood flow and stretch out the other parts of your arm.
Try not to rest your arms on anything for too long, they should hang from your shoulders, which in turn should be relaxed and dropped with a straight back. Resting on the armrest or desk all the time will compress tendons, ligaments and blood vessels. Your elbows should be a little more than 90degrees to your body, on a downward slant.
Review your position regularly. Most employers insist their staff take a workplace training module (usually computer based) once a year, it's mandatory in government offices in the UK where Workplace Risk Assessors are on hand to observe if something is flagged up by the training. You need to treat yourself as an employee and make sure you complete regular checks and training. Fine yourself if you don't do it!