Abstract: A non-crosslinked derivative formable by reacting at least one substituted or unsubstituted, saturated or unsaturated, mono-, di- or poly-carboxy, hydroxy or mercapto hydrocarbon with at least one cyclic unsaturated (thio)ether.

Abstract: An optical viewing tube having an eyepiece at one end and a viewing prism at an optical tip at the other end is provided with an optical system therebetween which will provide a focus for an object being viewed. A distance indicating disk or device on said tube is movable by a focusing mechanism to indicate the distance from the optical tip of the viewing tube to a viewed object. A camera is provided to be attached to the viewing tube to take a picture of the viewed object, and an eyepiece with a properly marked reticle is placed on the photograph taken, to indicate proper distances between spaced points on the object as seen in the photographs. The viewing tube is calibrated along its length so that tube penetration can be accurately known and a retention adapter is used with the tube to rigidly fix it in place. The retention adapter includes a compass rose which indicates the position of the viewing prism.