Thinkpads Forum

Recently I've experienced a small degree of mouse drifting when using the trackpoint. I did some research and the common "solution" is to remove the finger from the trackpoint when not using it, i.e. not resting the finger on the trackpoint. This solution assumes that the drift is caused by the trackpoint itself. In my case this was not the problem. After reviewing the way I use the trackpoint I discovered that the bottom of my right thumb was resting on the upper right corner of the trackpad, i.e. unconsciously touching the trackpad was causing the mouse drifting. Thus disabling the trackpad solved the mouse drifting when using the trackpoint.

Looking at how the Track Point (Ultra Nav) device works, according to this article, it works using a solid state strain gauge. (what I didn't know is that if you tap it, it acts like a left mouse click).

Nice little article on how solid state strain gauges work is here.

I guess another reason for mouse drift could be a spec of dirt in the mechanism preventing the strain gauge from completely moving back to its 'at rest' position.

Not directly relating to the trackpoint but rather the trackpad, I often find that if I operate the tpad with the palmrerst loose (ie not screwed to the base) then the mouse pointer jumps all over the screen.

From Wikipedia:

Touchpads operate in one of several ways, including capacitive sensing and conductance sensing. The most common technology used today entails sensing the capacitance of a finger, or the capacitance between sensors.

I guess this is due to some changing capacitance effect between the finger and pad as the palmrest moves slightly in relation to other parts of the laptop and causes this jumping effect.

Also the same can happen if I've just cleaned the pad, and again I guess it's the remains of moisture which is causing a changing capacitance or resistance effect between the finger and pad.

The Trackpoint will reset it's rest position if it is held in the same spot for a long time, like if you are resting your finger on it while waiting for something to happen. That means that if you take your finger off it will drift untill it re-calibrates. I guess that also means that a spec of dirt will not affect it permenantly. The touchpad does seem to have problems with moisture, if there is some condensation on it, or if your hands are wet, the cursor does seem to jump around.