Moment of Inertia (MOI) Also known as Rotational Inertia, MOI is a measure of a putter’s resistance to rotation (away from square to the arc) when acted upon by an outside force.
Stability The property of a putter in a condition of equilibrium (and square to the arc) or steady motion (and square to the arc) that resists rotational changes in its equilibrium or steady motion when acted on by an outside force.
The direct measure of a putter’s actual scientific stability is moment of inertia (MOI).
From a purely scientific perspective, Moment of Inertia (MOI) and Stability are not just synonymous; MOI and Stability are scientifically identical; MOI and Stability are exactly the same. But the marketing departments of major putter companies continue to describe stability as if it is independent of MOI. It is not. Any increase in stability will be reflected in increased MOI (as a scientific necessity).
The major putter companies continue to claim increased stability from a variety of design characteristics but insist that the actual MOI resulting from their design innovations is proprietary information. The advent of putting launch monitors will bring this dissembling to an end, eventually.
