Weighing resin mixtures instead of measuring
Not too long ago the only practical way to mix two part epoxies was to measure the volumes. You could use marked, different sized containers to measure 2:1 or 5:1 resin to hardener ratios or you could buy pumps. I have a pair of $300 lever handle resin mixture pumps I used (and cleaned and refurbished again and again) for decades.
Now it's a different era. For $20 - $30 USA dollars you can buy an accurate digital postal (or "kitchen") scale. Raka 2:1 resin has a resin to hardener weight ratio of 43:100
I put an empty yogurt container on top of the scale and then press the red button on my postal scale, which then zeros out a digital readout. I pour the needed amount of resin into the container and note the weight. Multiply that by weight by .43 and then put that much hardener into an other container. And then mix.
Sometimes I add the resin weight to the hardener weight and then pour hardener right into the resin cup while watching the scale. I stop pouring hardener when the readout reaches the combined weight. You do have to go slowly if you go that route. It's all too easy to pour too much hardener into the resin. And then you have to start making guesses.
I don't use my pumps at all any more. Weighing resin is the way to go. Which ever brand resin you buy (West, SystemIII, Raka etc) will have an 800 number you can call, in order find out what the weight ratios are. If not already printed on the bottle label.