Hi there
I see tortoise-licker has left his mark,
Just to let you know i'm using Sonix and have had no problems with it "despite what others say".
I will change markers later when i've had bit more use out of this reliable marker, just ordered a 16" thunderpig Barrel from E-bay $22 =cheap upgrade, that should improve my accuracy a bit.
There are plenty of sites with write-ups on the 'SONIX', try the manufactures site there's plenty on them.
(I know Tortoise will reply to this) hahaha
have fun
SHED-HEAD