What CG is
The center of gravity is where the plane balances. Too far forward and it flies nose-heavy and sluggish; too far aft and it becomes unstable or unflyable.
Chord percentage
CG position is expressed as a percentage of the wing chord: CG % = distance from leading edge ÷ chord × 100. A 200 mm chord with CG at 60 mm is 30%.
Reference chord vs MAC
On tapered wings the meaningful reference is the mean aerodynamic chord (MAC), not the root chord. The calculator computes % of the chord you enter — stay inside the manufacturer’s published CG range.
Where it is used
The CG Calculator does the math; the balancing guide walks through the physical check.