During thawing and freezing of a foodstuff several parameters influence its processing time. These are ambient temperature, thickness of products heat transfer coefficient at the surface, thermophysical properties of product, initial temperature of product, water and bound water contents of product. During definition of mathematical model of these processes, all these parameters are used to predict thawing or freezing time. In reality, however, ambient temperature is measured in certain accuracy; each system has a different precision, sensitivity and resolution. During measurement of thickness, one millimeter of mismeasaurement can be done very easily. Convection and radiation heat transfer coefficients are calculated from equations with certain assumptions or experimentally measured with some restrictions. Therefore for evaluation of a model and discussing its validation, such parameters should be also considered. In this study effects of small changes in process parameters due to imprecise measurement to thawing time are investigated and their counter effects to each other are discussed.