For hitobjects there are 512 'pixels' on the mappable X axis and 384 on the mappable Y axis. You can use this information to either make your own rulers (Temporary SB?) or remove the need for such rulers.
e.g., to get a hitcircle in the exact center, all you need is a circle at x:256, y:192 You can figure out whether objects are x 'pixels' apart from one another using those's method.