Edit: I'm wrong. Original wrong post removed, correct info follows.

Gear inches is the diameter of high-wheel wheel that would go the same speed as your vehicle for the same cadence. Since a unicycle is a high-wheeler with no rear wheel, it is its own gear inches. The diameter of the outside of the mounted tire is your gear inches.

Meters development (or inches development) is the distance you will travel in one complete stroke of the cranks, would would equal the circumference of the tire on a unicycle.

peace,
sam