Seat depth, measured from the back of the buttock to two inches behind the knee, because a seat that is too deep cuts into the back of the knee and a seat that is too shallow puts all the load through a smaller area.

Seat-to-floor height at the front, which depends on the length of her lower leg and on the height of every table she will ever need to get her knees under, including a school desk.

Back height, which for an active user is low — below the shoulder blade — because a high back stops the trunk rotating and rotation is how you push, and which on the chair we bought was an inch too high, which does not sound like anything and which is the difference between a push that uses the body and a push that uses the arm.

Rear axle position, which is the one almost nobody has heard of and which is the most important one on the whole sheet.