The production system which one operative worker performs all the processes of completing a product from an assembly to an inspection and packing is currently called the single-worker booth production system. It takes most time to complete a product at an early stage, but production time decreases gradually with the increase in the number of work and settles down about the stable time. The time is used as job standard time in work study. This phenomenon is called learning effect or experience effect. A power law function in the learning functions is well known as a learning curve model and the other function is an exponential function proposed by Pegels. In this study, the exponential function type of learning model is treated and the four methods estimating parameters A,B and C in y(x) = AB^x + C (0 < B < 1) which is suited to realities are proposed. Further, the validity for the proposed methods and the method of Pegels is confirmed by using the numerical example of the peg-board inspection and we discuss the fitness of the function in comparison with the proposed methods by using the residual square sum.