I do not have an explanation for why off is maximum but that appears to be the case.
The explanation is that the concept of "magnetic strength" came along after the concept of snap-to-grid was already well established. Contrary to the presumption (admittedly intuitive) that magnetism is what causes objects to snap to the grid, magnetism is what allows you to place an object a little bit off the grid, and
not have it snap back to it. The higher the magnetic strength, the larger the window around the grid lines becomes. So the idea is that if you don't want/need to be able to place objects off the grid, you should turn magnetism Off.
The problem is that "magnetism just isn't a very good metaphor for how this works. Really they should have just had a "Window Size" parameter. At 100%, the window would extend 50% of the grid interval to either side of each line, giving you normal snap behavior. Then you could have lower percentage settings where snap would only act within that smaller range around the gridline.
Another factor that makes this behavior hard to understand and take advantage of is that the "windows" represented by the Low, Medium and High settings are all quite small, they do not vary with snap resolution, and they represent a constant amount of screen real-estate (i.e. pixels), which means the higher the zoom level, and the lower your grid resolution, the smaller the window becomes, musically.
At maximum zoom in the PRV, the ±1/8" of screen real-estate (on my 22" monitor) with
High magnetism represents only ±13 ticks. Even with snap at a relatively high resolution of 1/16, this gives an effective "window" size of only 26/240 = 10.8%. With snap at a Measure in 4/4, you're down to 26 / 3840 = 0.7%. And with magnetism on Low, the window is down to ±4 ticks, or 8/3840 = 0.2% of a measure!
This is why it seems like snap does not work at high zoom levels with magnetism enabled. You have to be dragging pretty slowly to hit the tiny little magnetism window around the gridline, and not just drag right through it.
post edited by brundlefly - 2011/06/14 12:51:03