Because of their sophisticated design, adiabatic calorimeters record the true caloric properties of a substance. In contrast, the compensation of losses and, thus, the quasi-adiabatic behaviour of the more common isoperibolic differential calorimeters is achieved by balancing heat losses. Based on previously published models, a theory for isoperibolic differential calorimeters is developed which closely follows the actual measuring conditions. In particular, the relation between dynamic and static heat losses is addressed, and the limits for the compensation of losses are indicated. The investigation has resulted in the recommendation of measuring conditions which, if closely followed for various temperatures, allow the measuring error caused by non-compensated losses to be determined with the help of zero-line offsets, without the necessity of knowing the air gap thicknesses or the heat transfer coefficients that cause the error.