The bones are named Top, Middle, and Bottom for simplicity.

All bones are selected, multi-paint is active,
 but the bone combinations are covered at the different edge loops.

To do the test, paint over the vertices that are in the top ortho view
 with the provided Add brush (weight and strength 1.0)

For the first, highest set of vertices,
 you should be able to sample these weights from each different bone
 (Ctrl+LMB with the corresponding bone selected):
	Top weight: 	1.000
	Middle Weight:	0.667
	Bottom weight:	0.333

The second ring down will have
	Top weight: 	1.000
	Middle Weight:	0.667
	Bottom weight:	0.000

The third ring will have
	Top weight: 	1.000
	Middle Weight:	0.000
	Bottom weight:	0.333

And the fourth and final ring will have
	Top weight: 	0.000
	Middle Weight:	1.000
	Bottom weight:	0.500


For the next case, enable auto normalize.
 You can switch to the bottom ortho view for an unaltered set of vertices,
 but it will not change the final results.

Make sure all of the bones are selected.

Paint over the vertices in the view with the same Add brush as before.

The first, top ring will have:
	Top weight: 	0.5
	Middle Weight:	0.333
	Bottom weight:	0.167

The second ring down will have
	Top weight: 	0.600
	Middle Weight:	0.400
	Bottom weight:	0.000

The third ring will have
	Top weight: 	0.750
	Middle Weight:	0.000
	Bottom weight:	0.250

And the fourth and final ring will have
	Top weight: 	0.000
	Middle Weight:	0.667
	Bottom weight:	0.333


For any case:

Weights of zero should always remain zero.

Having only one bone selected should behave like a regular paint.