Thinking about it, if the clock runs backwards at the same rate, so -1 hour per hour, the rate of randomly being right is 2x the stand-still rate. This is also a linear function, at -1 its 4x per day, -0.5 is 3/d, 0 is 2, 0.5 is 1. When it runs true it is however very different, as it is either always exactly right (no offset) or never (with offset).
A backwards ticking clock appears accurate more frequently than a stopped one.
Thinking about it, if the clock runs backwards at the same rate, so -1 hour per hour, the rate of randomly being right is 2x the stand-still rate. This is also a linear function, at -1 its 4x per day, -0.5 is 3/d, 0 is 2, 0.5 is 1. When it runs true it is however very different, as it is either always exactly right (no offset) or never (with offset).
A broken clock running 6x its speed will also be correct much more often than a stopped clock.
Where I’m from the saying is a little different: “A broken clock is still accurate twice a day”
Same, my comment is an extension of that more common notion.