We present a theoretical model of a calorimeter, with particular reference to the Perkin-Elmer DSC-7, with the aim of emulating, in the simplest possible manner, the essential operations of this instrument. The basic idea is to assign a working transfer function to each of its fundamental elements: differential temperature amplifier, average temperature amplifier and programmer From these transfer functions we get the theoretical output of the calorimeter. This output is used to fit the unbalance that occurs when the calorimeter switches from isothermal to scanning state. Following this, we work out the transfer function of the calorimeter and evaluate it using the parameters obtained from the fitting. We then use this function to deconvolute the melting peak of indium samples and to interpret melting temperature dependence on the scanning rate.