Proove Ink cartridges
Proove International AB, Sweden, sells used ink cartridges for HP printers who perform very poorly in the EU.
 Cost pr page
A number 9 Proove ink cartridge equals the HP 57 Tri-Color Print Cartridge.
The nr 9 Proove cartrige as enough ink to print 60 15x10 color photos before one color is printed with less strength than it should.
hp-levels reports "approx. 15%" when nr 9 Proove cartriges are actually empty.