If you're not getting accurate quantities, you:

• Might be using a blown glass measuring container, which could be inaccurate.
• Might be requesting an amount below 4 oz (1/2 cup). Try reducing your faucet flow rate to improve accuracy at these small quantities.
• Might be requesting a very large amount, which cannot be filled before the automatic four-minute shutoff of your faucet. Make sure your faucet handle is set to maximum flow rate for large quantities.