If the clock is held at a constant 0.0ºc over a period of 24 hours, how much longer or shorter does the clock measure compared to a perfect clock?

If the clock is held at a constant 0.0ºc over a period of 24 hours, the clock will be exactly the same as the perfect clock because  it is at a constant 0.0 ºc for 24. Meaning there is no deviation on its reading

the 2 figures are congruent bc if you reflect abcd over the y axis then over the d axis the figures overlap