Decades ago, I saw a bit by a stand-up comedian lamenting shower temperature control. He noted that every shower, it seemed, had a dial on it to control the temperature with (literally) an infinite number of settings... but that the difference between ice water and liquid hot magma was a fraction of a degree.
Somehow, I found myself reminded of that this morning.
What I don't understand is why we're still stuck with this system. It's utter madness, so why do we persist with it?
Surely, it should be possible to construct a shower with better control than that. As far as I can see, what is wanted is a dual display, with the top showing the desired temperature (in degrees), the bottom showing the actual temperature, and a set of buttons allowing you to adjust the desired temperature in increments of 0.1 of a degree (or even less). For extra credit, the shower could even have a number of preset values - that way, if she likes the water at 38.2 degrees and he likes the water at 36.8 degrees, it's trivial to switch between them. And so you don't get another version of the "toilet seat" argument *.
It really shouldn't be beyond the wit of men to develop such a thing - electric showers already take in cold water, heat it to a desired temperature, and then feed it through, and all this adds is an additional sensor and feedback step. And you can already get wirelessly controlled showers (no, really!), meaning that the issue is clearly not with putting electronics close to a water source.
And there's another advantage, beyond mere considerations of comfort and safety. As things stand, every single shower is unique. The temperature dial on each and every shower, even two showers of exactly the same make and model, is slightly different. That near-mythical sweet-spot between freezing to death and your flesh melting is in a slightly different place each time.
But temperature is an objective measurement. Assuming proper calibration, 36.8 degrees on my thermometer is the same as 36.8 degrees on your thermometer. So, if we moved to a standard design where the user could input a specific target temperature, then all they would need to do is remember their preferred value (which isn't all that hard, really), and every time they found themselves staying at a Premier Inn they could just set that value, without having to endure painful experimentation or deeply unsatisfying showers.
* Incidentally, science gives us the correct answer to the "toilet seat" argument. Before flushing, you should put not only the seat but also the lid of the toilet down. And if you haven't been in the practice of doing that, you should also replace your toothbrushes immediately.