- var wanted_ticks = pixels / pixels_per_tick;
- var units_per_tick = Math.abs(b - a) / wanted_ticks;
+ // Get the maximum number of permitted ticks based on the
+ // graph's pixel size and pixels_per_tick setting.
+ var max_ticks = Math.ceil(pixels / pixels_per_tick);
+
+ // Now calculate the data unit equivalent of this tick spacing.
+ // Use abs() since graphs may have a reversed Y axis.
+ var units_per_tick = Math.abs(b - a) / max_ticks;
+
+ // Based on this, get a starting scale which is the largest
+ // integer power of the chosen base (10 or 16) that still remains
+ // below the requested pixels_per_tick spacing.