RUBIK'S CUBE
Speedcubing timer
A fresh scramble every solve — random-state too, as at a competition — the 15-second WCA inspection, the ao5 and ao12 averages worked out the way they are at a competition, and the +2 and DNF penalties. You hold the space bar — or your finger, on a phone — until the time turns green. Free, no sign-up: your times never leave your device.
Hold until the time turns green, release to start, tap again to stop.
How to use it
At the top is the scramble to apply to your cube: twenty random moves, with no pointless repeats like R R' and never three moves in a row on the same axis. Apply it, then hold the space bar. The time turns green when the timer is armed: release and it starts, tap again and it stops.
Every time drops into the list below. Select one and the +2, DNF and Delete buttons act on it: you need that when the cube was a quarter turn from done, or when the attempt went wrong and should not count.
The averages, worked out as at a competition
The ao5 is the average of the last five attempts with the best and the worst dropped; the ao12 does the same over the last twelve. It is not just any average: it is the WCA rule, and it is what makes the number comparable with anybody else's.
DNFs follow the same rule: one DNF counts as the worst and gets dropped, but two DNFs make the whole average a DNF. That is the part improvised calculators always get wrong.
Two kinds of scramble
By default they are twenty random moves, with the required filters: never the same face twice in a row, never the same axis three times. It is instant and fine for practice.
From the menu you can switch on the random-state scramble, which is the competition one. You get it the opposite way round from how it sounds: draw a cube at random out of the forty-three quintillion, solve it, and write the solution backwards. The first one takes about a second to build the tables; after that you stop noticing, because the next scramble is prepared while you are still solving this one.
The difference is not that the cubes get harder — I found no measurable difference there. It is that twenty random moves are a random walk twenty steps long, and a walk that short does not cover the cube evenly: some states stay likelier than others. Over 400,000 scrambles of each kind, comparing corner orientation against the distribution you can compute exactly, twenty random moves give a chi-square of 31, 43, 53 and 73 over four runs, against a 99% threshold of 18.5. The random-state scramble gives 6.1, 6.6, 7.1 and 11.5: uniform, as it should be.
Inspection
You can switch it on from the menu. These are the fifteen seconds in which, at a competition, you look at the cube before starting: past the fifteenth you get a +2, past the seventeenth a DNF. Practising with inspection on changes the way you look at the cross, which is why it is here.
Frequently asked questions
Are the scrambles the competition ones?
You can choose. By default they are twenty random moves, instant and fine for practice. From the menu you can switch on the random-state scramble, which is the official definition: draw a cube at random, solve it, write the solution backwards. The first one costs a second, after which the next is always prepared in advance.
What difference does a random-state scramble make?
It does not make the cubes harder: I found no measurable difference there. It makes the choice uniform. Twenty random moves are a random walk too short to cover the cube evenly, and it shows: over 400,000 scrambles of each kind, corner orientation compared against the exact distribution gives a chi-square of 31–73 for random moves, against a 99% threshold of 18.5, and 6–12 for random state.
Does it work on a phone?
Yes. Where there is no space bar you touch and hold on the time area, with the same behaviour: green when armed, starts on the release.
Are the times saved?
Yes, in the browser's local storage: close the tab and they are still there. They stay on your device, are never sent anywhere, and there is no account. The whole session can be cleared from the menu.
How do I apply a +2?
Tap the time in the list to select it, then press +2. The same goes for DNF and for deleting. Pressing again removes the penalty.
Is it free?
Yes, and there is no advertising and no tracking. It is a single page running in your browser.
How it is built
A timer looks like the simplest thing in the world until you write one. The delicate part is not the measuring — the browser clock does that — but when to start measuring: the right gesture is hold, see green, release. Anyone who starts the clock on the press hands out a few hundredths on every attempt.
The other part worth some care is the average. Dropping the best and the worst is easy; doing it with DNFs in the mix is less so, because a DNF is not a large time, it is a time that does not exist, and the rule treats it as the worst only for as long as there is one of them. It is five lines of code that almost everybody gets wrong, and exactly the kind of detail that repays reading the rules instead of guessing them.
If you need something bigger of the same cloth, the projects are here and so are the contacts.