Recovery of refrigerant

Chilly1 says :
"Look at the specific gravity say it is 0.85 for your refrigerant. Water is 1.0 so what will hold water at 1 kg will hold your refrigerant at 0.85 kg however refrigerants have a tendancy to expand when heated so we want to keep a space above the specific volume of refrigerant in the bottle so we usually use 80% as a guide for most refrigerants. So the calculation is (water capacity) times (specific gravity of your refrigerant) times 80% desired fill capacity.
And if you get an a compressor and braze some schrade vlaves on it and put your bottle in ice to condense the refrigerant just pump it in use your manifold set to isolate the tank and compressor and put a hand valve on the compressor inlet. Pull a vacume on the compressor and tank the tank will also need a hand valve, The open valves to compressor and tank a evac, close valve to vacume. Connect another hose to the frig with the gas you want to recover. then purge it (let a little out ) then open valves and turn on compressor runtuntil all the gas is out of the frig or the cylinder is 80% full. do not exceed 80% use a postal scale for a small tank. An Ice bath with salt in it will condense a at a lower temp..

Always use a cylinder rated at a high pressure than the refrigerant you are recovering and it must have a relief valve at 60 % of the cylinder rating"

I am recovering the refrigerant from an airconditioner but i do not know what i have connected the proper way to recover the refrigerant. And i only have the tools drawn so how do i tell if i have filled to 80 percent of the tank?

AND THE WAY OF OPERATION IS THIS I WOULD OPEN THE SIDE WHICH IS CONNECTED TO THE TANK SLOWLY TO LET REFRIGERANT FLOW INTO THE TANK.THEN I TURN ON THE COMPRESSOR. BUT NOW THE HARD PART IS HOW TO TELL WHETHER IT IS 80 % FILLED DO I PLACE IT ON A WEIGHING SCALE?