Controlling number of grid lines

I am having trouble with axes and grids in the y-direction.

I have a 3 rows x 2 colums figure and I like to have 5 major Y divisions or 4 grid lines for each of the graphs. 5 of the 6 graphs came out properly. For instance, for a Ymin=12, Ymax=17, I get grid lines at y=13, 14, 15, and 16. However, the 6th one isn't right. For a Ymin=-5 and Ymax=5, I get grid lines at y=-4, -2, 0, 2, 4 (but the origin does starts with y=-5). I want to have only 4 grid lines (at y=-3, -1, +1, 3). I tried many settings but the result is the same.

What should I do to get only 4 grid lines in the y-direction?



John Henry