What kind of pressure does it measure? Air pressure? Finger pressure on the touchscreen?

I have Samsung Spica I5700 that have capacitive touchscreen, and I used a touchscreen protector. Recently, I've noticed that the touchscreen often produces erratic movements, for example, if I put my still finger on the screen, the "cursor" will shake vigorously (sometimes very far off). This makes the touchscreen very unusable; countless of times I've accidentally flinged the page when scrolling, while touching the screen for small scrolling; countless of times, the screen registered scrolling as a zooming or unzooming; …

HTC directly updated over-the-air (OTA) from 1.5 android to 2.1 android firmware on my handset. Since that time, the touch-screen (which is miscalibrated) can no longer be recalibrated, because the menu item has disappeared. I have, of course, requested support from HTC via email, but I doubt that they will find an answer here, and I suspect my phone is now junk, unless some enterprising Phone-savvy person can figure out how to restore this thing. There is sadly no backup …

I've noticed that sometimes the virtual keyboard on my HTC Droid Eris can be very laggy. While composing a text message, it will take a second or more to respond to some button presses. Is there anything I can do to reduce the lag and make the virtual keyboard more responsive?