I had a problem with my mousing-arm going numb at the shoulder after about 3-4 hours of work. I noticed that I was lifting my entire arm off the desk as I moved my mouse around. I switched to a Logetic Marble Mouse, and have been very happy with it. Now I can lay the entire weight of my arm on the desk, and I only use my index (sometime adding my middle) finger to move the cursor around.
Also something else that I have noticed, is many people sit way too low at their desks. Here's some pointers that work for me.
1) My thighs are parallel to the ground when my shins are perpendicular to the ground.
2) I sit all the way "into" my chair so my back is supported by the chair. Many times however, I catch myself sitting at the very edge of my chair... bad.
3) My monitor is positioned so I can hold my head straight, glancing slightly down (maybe 10 degs) with my eyes, and the screen is perpendicular to my field of vision.
4) My keyboard and arm rests on my chair are positioned so my elbows are supported and my forearms are parallel to the ground. This meant I had to raise my keyboard, and my 1st ed SolidWorks for AutoCAD Users was the perfect height.
![[pc2] [pc2] [pc2]](/data/assets/smilies/pc2.gif)
"The attempt and not the deed confounds us."