Scleral lenses have gained popularity in the last decade. From a lens with limited viability for over 100 years to the fastest growing segment of the gas permeable lens market, scleral lenses have come a long way.
Mass and Weight. The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Definitions of mass often seem circular because it is such a fundamental quantity that it is hard to define in terms of something else.
On Earth we know the value of the gravitational attraction, so a measure of the weight (which is what a regular scale measures) gives us directly the mass. This is why in the common language weight and mass are often confused. But it space it makes a big difference. Objects can have a large mass, but weigh nothing. So how do we measure mass in space?