Sizing
To find your ring size at home, wrap a thin strip of paper round the finger at its widest point, behind the knuckle, and mark where it meets. Measure the length in millimetres: that's the inside circumference, and every ring page turns it into a size.
Measure at the end of the day, when hands are warm, and not straight after cold water. A band should slide over the knuckle with a little resistance and sit easy behind it. If you're between two sizes, choose the larger.
The Duet is two bands in two sizes, one for each of you. Giving a band as a surprise? Borrow a ring she wears on that finger and measure across its inside.