I was asked by our Chair to perform a cost analysis of the two brands of white board markers. I will use the following notation:
Q = Quartet disposable markers.
P = Pilot VBoard Master markers, which have replaceable cartridges.
(I will not even speak of Expo, because they suck.)
To compare volume of ink in each marker/cartridge, I drilled a few holes in a Q and drained it into an empty P cartridge. I allowed for loss of 10%, which I’m confident is a gross overestimate. The P cartridges are very close to right cylinders, so the fill height is proportional to volume of ink.
Q: Cost: pack of 12 for $11.10.
Fill height: 2cm + 10% for possible under-measurement = 2.2 volume units
Price per volume ink: ($11.10/12) / 2.2 = $0.42 / volume unit
P: Cost: $0.45 per cartridge
Fill height: 4 cm
Price per volume ink: $0.45/4 = $0.11 / volume unit
Another consideration is that the P markers (with one cartridge already in them) come in packs of 5 for $4.33. That works out to ($4.33/5) / 4 = $0.21 / volume unit, so still less expensive than Q even if we never change the cartridge.
I have generally found that P write better than Q. This might mean that P deposits more ink (per foot, say, of writing) than Q. If that’s true, then I doubt if P uses four times the ink that Q does.