All great points... I use a $30 digital scale from Bed Bath and Beyond. I brought it to work and checked it with some calibrated weights and it was accurate within 0.5 lbs up to 100 lbs. If you are weighing out 5 gallons of water, that gives you about a 1% accuracy. I don't think I could measure out 5 gallons of water in a container and be accurate within 1%. I use a tripod carboy drainer placed upside down on the scale to elevate whatever it is I'm weighing so I can see the numbers.
As for the variation in volume at different temepratures, it doesn't matter. For me it makes sense that in batch sparging it's better to calculate strike temepratures by knowing the mass of additions, not the volume.
As for the variation in volume at different temepratures, it doesn't matter. For me it makes sense that in batch sparging it's better to calculate strike temepratures by knowing the mass of additions, not the volume.