We have carried out pitch measurements in the smectic C* phase of a commercially available room temperature ferroelectric liquid crystal, SCE12 (BDH), as a function of pressure. An optical diffraction technique has been employed for the purpose. The diffraction patterns were recorded using a video camera as a 2-d detector. The data is extracted using a frame analysis hardware-software combination. A detailed description of this method is presented. The results show that the application of pressure not only affects the absolute value of the pitch but influences its temperature dependence also. Measurements of spontaneous polarisation also show a similar feature. Possible correlation between the two results is discussed.