I found this on the internet, hope it helps....
Touch screen Calibration.
Method valid for NavCore versions until 8.051.
A manual method to correct the calibration of the touchscreen
input device of any all-in-one TomTom systems consists in creating a file called calib.txt
(e.g., with notepad) and saving it in the main directory
of the TomTom disk memory (e.g., the SD card
; the same directory of the ttsystem file).
calib.txt should include one line with four numbers separated by a space
MinX MinY MaxY
Notice that the ‘x’ sequence (max, min) is inverted than the ‘y’ sequence (min, max). MaxX > MinX and MinY < MaxY.
For instance, the file can include:
928 118 107 912
Each TomTom device has its own most appropriate sequence.
In order to compile the file with default data, one method could be to perform a TomTom reset (or to eject the SD card), powering on the device and holding down the ON button for a few seconds until a unit status screen appears. The line named “Touchscreen calib. data:” will include four numbers that in sequence represent MinX MaxX MinY MaxY; these numbers can be used to fill the configuration line of calib.txt remembering to swap the first two ones. For example, if the unit status screen returns 118 928 107 912, calib.txt has to be saved with 928 118 107 912.
Tuning can then be done by adjusting these numbers until the touchscreen is calibrated. Distortions like screen rotation, trapezium and rhombus correction cannot be achieved with this method even if tuning these parameters can provide an acceptable touchscreen management even in presence of distortions; the best screen to tune the calibration is exploiting the soft keyboard of the NavCore application.
For instance, in my old TomTom GO Classic device I realized that, after activating the NavCore soft keyboard, when moving vertically (Y axis) the cursor appeared calibrated, while the horizontal movements (X axis) prevented to manage the left and right key columns (especially in the left bottom corner positions). So, I left the last two digits unaltered and, after some tests, I successfully used the following values: 805 200 107 912.
Method valid for NavCore versions post 8.051.
For NavCore versions 8.2x and 8.3x, use the same method as mentioned above, with these small differences:
the file should be named cal.txt (and not calib.txt) and should again be positioned in the main directory of the SD (or HD) drive of the TomTom system (e.g., the same directory where ttsystem can be found). Besides, the four numbers included in the file should have a different sequence than what previously described for versions until 8.51; cal.txt shall include the following sequence: MaxX MinX MaxY MinY (notice that also MaxY precedes MinY).
For instance, cal.txt could include the following four digits: 928 118 912 107
Again, these numbers are specific of each TomTom single unit.
E.g., my TomTom GO Classic correctly runs 840 245 912 107.