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A variation of the Jelinski/Moranda model is described. The main feature of this new model is that the variable (growing) size of a developing program is accommodated, so that the quality of a program can be estimated by analyzing an initial segment of the written code. Two parameters are estimated from the data. The data are: a) time separations between error detections, b) the number of errors per written instruction, c)the failure rate (or finding rate) of a single error, and d) a time record of the number of instructions under test. This model permits predictions of MTTF and error content of any software package which is homogenous with respect to its complexity (error making/finding). It assists in determining the quality, as measured by error contents, early on, and could eliminate the present practice of applying models to the wrong regimes (decreasing failure rate models applied to growing-in-size software packages). The growth model is very tractable analytically. The important requirement for applications is that the error-making rate must be constant across the entire software program.