What is a Coffee Refractometer?

In short, a refractometer measures extraction percentage in a liquid, and with a little math can tell you how well extracted your coffee is. I need to calibrate this one as 11.29% is definitely low for espresso, so I'll download the app and figure out how to get good and accurate readings.
Will be doing a video about whether a refractometer is a useful tool for the every day home espresso lover, what it's good for and what to do with the information you get from it.
#espresso #homeespresso #homeespressomachine #coffee #coffeerefractometer