My sub-ten-euro Sigma BC1509 gives me the data to calculate average speed, and I'm sure one of the other dials will give me the average as a worked result if I cared enough to spend the time to find it, but I ride almost exclusively on hills, so the average for the whole ride isn't as much use as how long I took up a kilometre-long hill while not exceeding the permitted heart rate.
Polar Beat, the Bluetooth app that comes with the Polar H7 chest belt, assumes all cyclists are roadies, and thus takes every journey as a "training session" on a closed circle, and by default, unless you specify a different "lap distance", gives you a verbal report via your phone every kilometre or mile (depending on your setup choice of metric or imperial measures) in whatever form you find useful among several worked results of time/distance. The one I find have it permanently set to is "x minutes for the last kilometer", since I aim for an average in the hills of 15kph -- rather than Anto's impressive 15mph -- which is a speed my riding companions can keep up with. So any report of more than "4 minutes" causes me to slow down, and any report under "4 minutes" and I speed up a bit.
My pedal pals were at first startled by Polar Beat's verbal report via the phone every four minutes, glancing worriedly at the hedges for the source of the voice in the burning bush, but soon started asking me to repeat it louder...
That it is a verbal report is important, because the earlier Polar Beat app's marginally useful screen on the phone has been redesigned by a non-cyclist who fancies himself a "cutting edge" designer to be totally useless to cyclists -- I rate it "actively hostile" --, giving all the information equal value with equally small numbers, squeezing eight separate number sets into the top of the screen, and making some of them pale blue and others red and some even yellow, a totally unreadable mess. It may be possible to verbalize some other numbers; I just don't care enough to discover how. Polar Beat is free to owners of Polar heart rate belts; actually, it is free to everyone, but there is no guarantee that it works with non-Polar heart rate senders (it didn't for instance work with some Chinese belts I was given to test); it works very well with Polar senders, except that the wretched screen makes it near useless for keen cyclists who like instant access to a gazillion numbers though, to be fair, that condition is aggravated by the uselessness of phone screens outside, especially in sunlight.
This is what makes the Sigma cheap series of wired computers so great, that it was clearly designed by a cyclist, so that there are only two large, bright numbers on the large screen at any time, one of them always being the current speed, and that all the other numbers will appear either at the press of the single button, or any one of them can be held on screen by simply setting the thing to non-scrolling, or will scroll onto the screen at a known interval, so that the computer doesn't claim your attention except intermittently. It's an amazingly simple, ergonomic setup; I couldn't design it better myself. Well, except for this, which is a totally unreasonable demand of so inexpensive a device: If the button were remote, the dial could be mounted in the centre of the bars and the button next to your thumb. As it is, the whole thing is most conveniently operated from next to the gear control (mine is actually mounted on top of it), where the single large button falls naturally under your thumb, so that you have to turn your head very slightly to read it. On the other hand, I find that I rarely want to operate the button while riding, so the bike computer could be mounted in the centre of the handlebars, except that where I was trained as a psychologist we had a noted ergonomist on the staff with whom I got along particularly well, so I just purely hate taking my hand off the grip, even if rarely, to operate any device.
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What all this proves, besides the obvious fact that cyclists differ in their demands, is that tailoring a bike precisely to a cyclist's needs and desires takes a lot of thought on what the novice might consider very minor details. It took me twenty years to get to a bike that doesn't irritate in any respect. Without the internet providing access to other thoughtful cyclists of vast experience it might have taken forever, or be impossible.