you want to get a digital scale that measures in grams with a minimum accuracy of 0.1 grams. if you can find ones with 0.01 or 0.001 grams for relatively cheap, those would be great also. but if you're going with the PPS-Pro fert method, 0.1 is sufficient.
you can find them online, e-bay, hydroponics shops, or in the kitchen gadgets section. that's where i got mine from.
Thanks Guys Just what I am looking for I seen them on ebay but did not know which one was good. And yes Freydo I was planning on trying the PPS-Pro fert method. I have a low/med light 55gal set up no CO2 I use Excel what do you think about that method for this set up. Thanks again
using excel as your carbon source will be fine for your planned light levels, but for the long run, it will be quite expensive. it would be cheaper to look into going DIY or saving up for a pressurized system if it's not in the budget at this time.