'It is all right for a clock to run fast or slow at times, so long as it is calibrated against the sun, and set right. The sun may come out only once in a fortnight. It is enough. A few minutes' light around noon is all that you need to discover the error, and re-set the clock – provided that you bother to go up and make the observation. My parents somehow knew this, and did not become overly concerned at my strange enthusiasms. For they had confidence that they had taught me how to know when I was running awry, and to calibrate my behavior.'