The objectives of this work package are: (i) to measure kQ,Q0 factors for at least 4 types of ionisation chambers and at least 8 beam qualities, ensuring direct traceability of the kQ,Q0 factors to primary standards of absorbed dose to water; (ii) to calculate kQ,Q0 factors for these beams using several validated Monte Carlo codes; (iii) to compare the measured and calculated kQ,Q0 factors for kV x-ray beams, and to provide IAEA with a validated consistent new dataset of kQ,Q0 factors with target standard uncertainties better than 1.0 %.