The most robust watch crystals are made out of sapphire glass. Only diamonds and carbide is harder and can scratch sapphire glass. Of course there are other materials such as some metals and stones which will scratch your sapphire glass crystal, so it is not wise to expect the watch to handle any abuse without getting marked. Sapphire has one downside though, it is highly reflective. Some watches receive an anti-glare coating to compensate for this, but sadly this coating is less hard and will scratch more easily.

Digital watches and clocks have a digital display. That is what makes them digital watches and clocks. Whether they record time in a digital or analogue fashion is irrelevant. A digital display will not point out the current time on a display of all times possible, as it does in an analogue watch, but it will only show the digits of one time. Nowadays this usually happens via LED or LCD display, but that has not always been the case. Digital watches have been around long before the electronic display was invented. They used turning disks or cylinders behind a mask that would only show one digit at a time. Or airport-style flip-card mechanics were used.

Water tightness or impermeability, surprisingly enough, is the degree to which you can expose your watch to the element water. A watch can be water repellent to a variety of degrees, from surviving the odd splash, to keeping the watch fully functioning long after your crushed body has hit the ocean floor. Please note that these are always theoretical values. Water behaves very differently at different temperatures and with varying salinity. So we took our crayons and made you this rough guide (which, by the way, is in no way legally binding and we will not be held accountable for your watch if you ruin it):



FYI: 10m is 1 bar is (roughly) 33 ft is (exactly) 0.986923267 atm