A Bose-Einstein condensate (BEC) interferometer on an atom chip is capable of making an absolute force measurement. The author demonstrates this by making an absolute measurement of the gravitational acceleration g. Two interferometer arms are implemented by splitting a BEC into two symmetric wells using radio-frequency (rf) adiabatic potentials. The independent control of the rf currents running through the chip surface allows to change the polarisation of the rf field and hence the orientation of the double well potential. Tilting of the system with respect to the horizontal introduces an energy difference and the relative phase between the BECs starts to evolve. After moving the atoms back to their initial position and overlapping the clouds in free fall the resulting phase exhibits in the interference pattern. In order to derive a number for g from experimental results a detailed analysis and understanding of the interferometer scheme is essential. ukryj opis