Differential dilatometry is a technique for precise measurements of the thermal dilatation of materials. A procedure has been presented for calibration of the differential dilatometric measurement signal (length change as a function of temperature), both upon heating and cooling. Measurements of the thermal expansion of pure iron up to 1223 K have been performed by a high-resolution differential dilatometer (resolution in length measurement of about 10 nm). The magnetic contribution to the length change has been introduced for the first time in an analytic expression for the linear thermal expansion coefficient of ferritic iron. The dilatation signal has been calibrated on heating and cooling using a sapphire specimen for which recommended dilatation data are available. The ferro- to paramagnetic transition (characterized by the Curie point temperature) has been adopted successfully to calibrate the temperature in dilatometric measurements upon heating and cooling. (C) 2003 Elsevier B.V. All rights reserved.