There are four types of crosses:
A Full Cross fills a whole grid square. Parts of a full cross (Quarter Cross, Half Cross Forward and Half Cross Backward) can be placed or removed for quarter, half and three-quarter crosses.
A Half Height Cross is a cross in the top or bottom half of a grid square.
A Half Width Cross is a cross in the left or right half of a grid square.
A Mini Cross is a small cross in any corner of a grid square.
When drawing crosses, any type of cross can replace all or part of any other type of cross. The size of the currently selected cross type determines how much of a grid square will be replaced or erased.
Backstitch and French knots are not affected by drawing and erasing crosses.