Estimating Thickness
A lens clock can also be used to estimate the thickness of thin objects, such as a hard or gas-permeable contact lens. Ideally, a contact lens dial thickness gauge would be used for this, but a lens clock can be used if a dial thickness gauge is not available. To do this, the contact lens is placed concave side up on a table or other hard surface. The lens clock is then brought down on it such that the center prong contacts the lens as close to its center as possible, and the outer prongs rest on the table. The thickness of the lens is then the sagitta in the formula above, and can be calculated from the optical power reading, if the distance between the outer prongs is known.
Read more about this topic: Lens Clock
Famous quotes containing the words estimating and/or thickness:
“I am sure that in estimating every man’s value either in private or public life, a pure integrity is the quality we take first into calculation, and that learning and talents are only the second.”
—Thomas Jefferson (1743–1826)
“For his teeth seem for laughing round an apple.
There lurk no claws behind his fingers supple;
And God will grow no talons at his heels,
Nor antlers through the thickness of his curls.”
—Wilfred Owen (1893–1918)