The general principles of the bonded metalectric strain gage are given, and some specific applications to certain general problems are discussed. The variables in the measuring system are considered, the importance of each is shown, and the choice of the proper units for solving a given type of problem is indicated. Formulas are given as references for any design work the reader might wish to undertake, and derivations not already in the literature are presented. Some data concerning various instruments are reported as an indication of the results which can be achieved and to point out certain important differences which result from this type of measurement, as opposed to data obtained on conventional equipment.