Why can't I find the "antilog" format for labeling my axis ticks?

Prism only gives this choice (e.g., to alter the X-axis labeling, "Change... Axes: Range and Ticks... Numbering/Labeling Format" in version 3, "Change... X Axis... Numbering/Labeling Format" in version 4) when the space between ticks is 1. If your increment is a different number, then Prism does not offer the choice of writing the numbers as antilogs.