The pD of heavy water is generally measured using pH electrodes giving a pH (apparent) value, or pHa, and at various temperatures a true acidic pD can be estimated from the directly pH meter measured pHa, such that pD+ = pHa (apparent reading from pH meter) + 0.41. The electrode correction for alkaline conditions is 0.456 for heavy water. The alkaline correction is then pD+ = pHa(apparent reading from pH meter) + 0.456. These corrections are slightly different from the differences in pand p[OD- of 0.44 from the corresponding ones in heavy water.