In other words, he wished to have a margin at the other end, for he did not want a mutiny when he was perhaps within a few leagues of his destination.

On this day he notes that the raw and inexperienced seamen were giving trouble in other ways, and steering very badly, continually letting the ship's head fall off to the north; and many must have been the angry remonstrances from the captain to the man at the wheel.

Altogether rather a trying day for Christopher, who surely has about as much on his hands as ever mortal had; but he knows how to handle ships and how to handle sailors, and so long as this ten-knot breeze lasts, he can walk the high poop of the Santa Maria with serenity, and snap his fingers at the dirty rabble below.
On Monday they made sixty leagues, the Admiral duly announcing forty-eight; on Tuesday twenty leagues, published as sixteen; and on this day they saw a large piece of a mast which had evidently belonged to a ship of at least 120 tons burden.

This was not an altogether cheerful sight for the eighteen souls on board the little Nina, who wondered ruefully what was going to happen to them of forty tons when ships three times their size had evidently been unable to live in this abominable sea! On Thursday, September 13th, when Columbus took his observations, he made a great scientific discovery, although he did not know it at the time.
He noticed that the needle of the compass was declining to the west of north instead of having a slight declination to the east of north, as all mariners knew it to have.

In other words, he had passed the line of true north and of no variation, and must therefore have been in latitude 28 deg.N.and longitude 29 deg.