When trying to calibrate the printer (media sensor) the print ends up starting and stopping at the wrong place on the label. The printer seems to know how long it is between the gaps but then the printer stops at the wrong position (not at the correct tear position). Can anybody help me?

SOURCE: label not advancing to tear-off perforation

Try this to have the printer auto-sense the size of the labels:
1. Make sure that printer power is off.
2. Press and hold the feed button.
3. Turn printer power on.
4. When the status light blinks, release
the feed button.
5. The printer advances the media to
measure and verify the length of
individual labels or tags. The printer
then prints a status summary and
remains in diagnostic dump mode.
6. To begin normal operation, tap the
feed button. The printer prints "out of
DUMP" and advances a label.

SOURCE: Printer not calibrating correctly

Reset it to factory default.

SOURCE: Zebra 105SL label issues

I am surprised that you are using that sequence of buttons to solve this problem. I am pretty sure that they want you to go into the "Media Sensor Calibration" setup in the config menu. It is a bit more complicated than what you have described. I also believe that the size of the gap on two of your labels might be out of tolerance (they are usually 1/8" gaps between the labels). The black marks are a problem for the transmissive sensors. You may need to move the transmissive media gap sensor (remember it has two parts: upper and lower). I would usually setup mine for a place beyond the black mark so that you are looking at just the white paper.

To start out:
1. Load the backing of a 6" strip of media (no label attached).
2. Remove a ribbon (if you usually use one).
3. Close the printhead.
4. Press SETUP/EXIT and then NEXT/SAVE until "Media and Ribbon Calibrate" appears.
5. Press "+" to start the calibration procedure. You should see the "Load Backing" in the LCD Display. You already have the backing loaded so continue to the next step.
6. Press "+" to answer the message and the next screen should say, "Remove Ribbon". You have also removed the ribbon.
7. Press the "+" to continue. You should see the screen say, "Calibrating Please Wait". After the sensors are setup by the machine a new screen should appear, "Reload All".
8. Open the printhead, and move the labels until they are loaded correctly to print. Smooth out the ribbon and load it correctly.
9. Withe media and ribbon now loaded, press "+" to continue and the machine should say, "Media and Ribbon Calibrate".
10. Press the Setup/Exit button once. It should say, "Save Changes Permanent". Press Next/Save to finish the process.
11. Do a normal calibration of your stock and print a label.

You are done. The machine will run for the labels you have setup the sensors for. Unfortunately, you must do this for each of the media types. To automate this, you could run a Configuration listing, capture the settings you just created for each type of label. Take these to a programmer to have them send the setup to the machine before the job. This is beyond the scope of this type support to really help you.

SOURCE: TLP 2844 GAP sensor problem (I guess)

I had the same problem. I found out later there was a small piece of label sticking against the sensor, thus blocking the sensor from sensing the end of the label. As soon as I removed the label (open the cover, it is on the top part) it immediately started to work as usual. Hope this helps.

SOURCE: When calibrating, it onlt feeds a couple labels

Use the Menu system to calibrate, follow the instructions and it should calibrate with New settings. Calibration by setting it to calibrate on head close or bootup only loads factory settings.