Gold-plated Quartz Slimline II by MONDAINE, ca. 1987

Note the clever groove
next to the 11 o'clock lug (lower right). This I found on other Mirexal (manufactured by MONDAINE) watches. For snap-on case backs this makes really a lot of sense. You can see the tiny mark from my Bergeon opener (the opener is just right to the plastic tweezer in the centre of the picture) just where the light brightens up that half moon shaped groove. This case back sat very tight, thus the mark. I could not figure another way then to risk a little mark in that groove. Plastic or covered tools or a screw driver would have slipped and probably meant a bigger risk. Of course I had placed a paper into the groove before using my favorite Bergeon opener. Maybe one could file off the relative sharp edges of the tool, but then of course, one loses stability by having a smaller foot area to press.
Always be careful with tight sitting case backs. Once you slip and the case back jumps open and the screw driver slides accross the movement, you can only pray that you did not cut the coil. Most quartz movements are probably "destroyed" this way. This is when your shopping mall "watchmaker" - gnawing his lower lip - says, sorry, the watch did not jump start. The movement is probably too old Of course there are a lot of good watchmakers in the mall. Do not get me wrong here. I have seen - especially in large department stores around Bangkok - a scaring negligence, a really scary collection of tools and a couple of persons with definitely no passion or respect for watches. Maybe it is the low pay, maybe it is the lack of a proper training. I am just telling you, if you think you want to save a couple of bucks when quickly changing the battery: better be aware that the marks left could reduce the value of your watch more then if you went to a real watchmaker that charged a bit more.