—Dr Kalenak1,2 should be complimented for his vigilant stewardship of precise ophthalmic terminology. He is, of course, correct that a gram is a measure of mass, and the phrase "grams of force" implicitly includes the effect of the earth's gravity, as does the commonly used phrase "millimeters of Mercury." The basis for the confusion about units of mass and force probably originates from the English system, in which a "standard pound" is a unit of mass, yet a "pound of force" is the force created by the action of gravity on a standard pound at sea level at 45° latitude. The confusion is perpetuated as we stand on our bathroom scale and read our weight (or force created on our mass by gravity) in pounds and kilograms. How can this be? In this context, a pound is force, but a kilogram is always mass. Should not the
Britt JM, Clifton BC, Barnebey HS, Mills RP. Grams of Force-Reply. Arch Ophthalmol. 1991;109(10):1346. doi:10.1001/archopht.1991.01080100026017
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