The last time we had our watch batteries changed, my wife and I each went to different jewelers and each paid about $25 for a battery replacement.  We had no choice, since we had no way to press the watch back on if we opened it to change the battery.

Although this watch case press had no instructions, it is straightforward and simple to use.  You use the concave nylon dye on the bottom, with a diameter that fits OUTSIDE the crystal, so the crystal does not break.  You are supposed to use one of the flat dies on top, the same size as the watch back, to press the back on.  However, my watch back is convex and I found that I had to use a concave nylon die to press the back, instead of the flat die.  Once I switched to the concave die for the back, the case clicked together immediately with very little pressure required.

This is made out of heavy duty die-cast metal and I expect it will last the rest of my life.  It will save a lot of money on battery replacements!