The length of the eyeball (either longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors. Most people have one or more of these conditions. The cornea and lens bend (refract) incoming light rays so they focus precisely on the retina at the back of the eye.
BF series Composite strain gauge. This gauge is designed for measurement on composite materials. It has a specially designed grid configuration to reduce the tightening effect of the gauge to the specimen. As the temperature compensation is available for material with thermal expansion coefficient of 3, 5 or 8ppm/Â°C, this series is recommendable for ceramic, carbon, and composite materials.
A type of quasi-experimental design that is generally better than either the nonequivalent groups design or the pretest-posttest design is one that combines elements of both. There is a treatment group that is given a pretest, receives a treatment, and then is given a posttest. Quasi-experimental research involves the manipulation of an independent variable without the random assignment of participants to conditions or orders of conditions. 2  Among the important types are nonequivalent groups designs, pretest-posttest, and interrupted time-series designs.