Mass balance at a particular location on the glacier, for example at an ablation stake or a snow pit. The point referred to is at the top of a vertical column through the glacier. Most measurements of point mass balance are actually measurements of surface mass balance. That is, they exclude the internal mass balance and basal mass balance, which are either assumed to be negligible or corrected for later, and the flux divergence of the column. In the absence of an overriding reason for a different notation, point balances are indicated by lower-case letters, for example bw for the winter balance, while glacier-wide balances are denoted by upper-case letters, for example Bw.