Exercise 2: sample answer

3 seconds a day over 60 days is 180 seconds, which is 3 minutes of time error.

Using the table in the chapter, 4 seconds of time is about 1.9 km at the equator, so 180 seconds is 180 / 4 = 45 units of 1.9 km, about 85 km (check; one degree of longitude is about 111 km at the equator and 4 minutes of time is one degree, so 3 minutes gives about 83 km).

Both routes give an error in the region of 80 to 85 km, far greater than the half a degree (about 55 km at the equator) the Longitude Act called for (check the terms). In practice navigators knew the rate at which their chronometer gained or lost, and allowed for it, so a steady error of this kind could be corrected; it is the irregular drift that does the harm.