Well, I posted about some stuff before, but there are SH*Tloads of those digital pocket weighing machines (look like a calculator) on e-bay - I think it'
s in the Industrial&Business>Science>Instruments section or something. Man - you'll be surprised what you can find there - they ship fast and it's DEFINITELY cheaper than buying in stores . Hope that helps.
As for judjing by eye - I donno man - you can never be sure - cos sometimes it's tightly packed and sometimes it's more loose - so yeah, better buy a small weighing machine . I also agree w/ duppy man - I mean what's better a full Oz of shwag or just a bit short of Oz of good bud