If your height gauge on/zero/off button stops working, there's no need to send your tool to a repair man and pay plenty of cash to get it fixed!

Before doing anything you'll need to remove the battery. Then you take a X-Acto knife (or similar) and carefully peel of the ISO sticker on the backside of the tool.

Beneath the sticker you'll find the hidden screws for the plastic hood.

Be sure to lock the lock screws on the scale before removing the gauge. Be careful not to lose any of the small screws!

Remove the two copper plates and polish if needed.

I used 3M's red scotch bright to polish them. Be careful not to fold the thin copper!

Remove the five tiny screws on the backside of the PCB...

...and remove the data port lid as well before you try to take out the PCB.

First lift the PCB straight up as far as possible...

...then skew it a bit...

...and finally try to pull it out. You might need to give it a push via the data port.

Cut a piece of adhesive aluminum tape.

Use a pair of tweezers to remove the backing of the tape and to place it on the black surface of the pushbutton.

Apply a little bit of pressure to make the aluminum stick properly.

Although I used adhesive tape, I added a little bit of CA-glue to make sure that the aluminum would stay in place.
If you don't have aluminum tape, household aluminum foil and CA-glue will work just as fine. Don't forget to roughen the surface before adding glue.

No need to despair if the LCD comes off from the PCB, just place it in the plastic hood...

...and put the pink foam pieces as shown in the photos.

Now it's time to mount the PCB back in the hood. Don't forget to put all pushbuttons in place and the data port lid as well! When mounting the PCB, just reverse the same procedure as you used when you removing it.
Put all six screws back in their holes on the scale, the two short ones are to be placed in the middle holes. Then you put the thin copper plates back in its positions...

...carefully put on the plastic hood and screw it tight.

Your digital height gauge should now be working correctly and is ready to use!

About repairing other soft pushbuttons

You can of course use this method on similar types of pushbuttons on various things, e.g. TV, video and DVD remote controls.
In general many of these soft pushbuttons have this type of black conducting material, and if you push them too hard the conducting surface will eventually be worn out.
So be gentle and they will last longer.
Best of luck with your repairing!