For me, getting a refractometer was one of those upgrades that made a lot of difference. With a refractometer you need a sample size of two drops. I figured that this would pay for itself in beer savings alone. I also had just broken my hydrometer and came to the realization that hydrometers are made of breakable glass that can break! 🙂
With the aid of calculators – get a Free Non-Expiring Brewfather Trial Account – Refractometers can be used to measure gravity throughout the brewing process.