so. you want to know about... watches. little devices that keep time. maybe you're rich enough to consider them assets; maybe you want something that goes with your vestments; maybe you just need to tell the time quickly. sure. this guide will cover the stuff you need to know, and if you want to know more, you can check out the resources on the bottom.
animals have always been aware that the sun's apparent motion is roughly constant. the earth spins in its orbit around the sun, and when the earth makes a complete rotation of around 24 hours, we call that a day. meaning that on any given point on the earth, around twelve hours is spent under the sun's direct rays, and around twelve again is spent under rays reflected from the moon.p>
a long story of evolution short, light is important to animals because they use light to see. however, mother nature never bothered with giving animals accurate internal clocks, because the length of daylight isn't really constant. the earth's movement around the sun is skewed in a bunch of different ways, which means that unless you live exactly on the equator, daytime is longer during summer and shorter during winter (for example, you get a few more hours of daylight in summer if you live in California; or days if you live at the poles). not to mention that a day isn't exactly 24 hours, because of the moon's pull on the earth slowing it down. feel free to ask your friendly astronomer about these issues.
moving on. we don't know exactly what happened when humans came onto this earth. you likely know that ancient knowledge was a mixture of science, religion and philosophy. we have little records of that period, so we don't know a lot about how they perceived the concept of time, other than the wealth of sun gods. we do know, however, that people invented a few different devices for keeping time. the most iconic is the sundial: it's a freestanding asymmetrical structure, and the sun's movement casts a different shadow depending on its place in the sky... measure the movement of this shadow, and you can measure time.
some sundials use triangles, some use rods, and some use a nifty thing called an analemma which looks a bit rude. other timepiece options include the water clock, the burning rope, rudimentary gravity- and ice-powered gears, and other creative solutions. until galileo (the same guy who told the church that the earth goes around the sun) famously noticed in the late sixteenth century that a pendulum always swings with a constant period, no matter the weight or the height you drop the weight from—it only depends on the length of the rope and the force of gravity. he didn't work out all the details, just as he didn't perfect the pendulum clock; but people soon realised that this was a vastly more efficient method than anything that had come before.
by the eighteenth century, the clock industry had engraved itself into the economy: first selling their products to sailors (as you can calculate your position if you know your current time and the time at home), then to factories that needed clocks to organise the newfangled "production line". the intricacies of this socio-economic change are too many to list, so please find an expert on pendulum clocks if you're looking for that information.
moving on. we mentioned earlier that there were rudimentary geared clocks. those eventually became the pocket watches of the eighteenth and nineteenth century. they had a spring that would very slowly unwind, and this constant application of elastic energy powered the clock. a pocket watch at the time was quite expensive—about a month of minimum wage. this meant you could only afford it if you were very wealthy, hence the stereotype of posh people having pocket watches.
then, in the 1860s, somebody called Aaron Dennison had the bright idea of developing a simple pocket watch, machine-built and not "jewelled" (using precious stones as ball bearings). suddenly a watch only cost several days' wages. and he couldn't have timed it better—the American Civil War broke out, and there was huge demand for this new product. the watch was now in the hands of the masses.
soon enough, soldiers found it quite inconvenient to take a pocket watch out whenever they needed to tell the time. depending on who you ask, it was a nameless WWI soldier, or a famous watchmaker, or field watch companies, that invented the wristwatch as we know it—a stout cylinder held to your wrist with a taut strip of material.
more technological improvements were soon to come. [scientists] discovered that when you put energy into quartz, it vibrated at a constant speed, something called the piezoelectric effect. it's possible to harness these vibrations to power a clock. then people invented the semiconductor, and now there are smartwatches. then people invented the atomic clock, and we redefined time itself.