Tallie,

Straight from the Help Index.

The Periodicity page is located in the X-Axis Properties dialog. Choose X-Axis from the Format menu, or right-click on a chart's x-axis and choose X-Axis Properties from the shortcut menu.
Use the periodicity page to specify the periodicity of the data. For example, if your chart contains daily data, you could change the data into weekly bars. Or if your chart contains tick data, you could change it to hourly bars. If your chart contains online data, you can change the periodicity to anything available from your online vendor. If your chart contains local data, you may only change the periodicity upwards (e.g. daily to weekly, 5-minute to 30-minute, etc.).

When the periodicity is changed, the same number of periods is retained.
Volume and open interest are summed over the new period. For example, monthly periodicity displays the sum of the entire month's volume.
The Other periodicity option allows you to control the number of periods over which to compress the data. This allows you to view the data using non-standard periods. For example, a periodicity of eight periods with daily data loaded would display a price bar every eight trading days.

You can also change the periodicity by right-clicking on the x-axis and choosing Periodicity from the shortcut menu.
You can also click the Periodicity button on the chart toolbar to change the periodicity.
You can also change the periodicity with your Microsoft IntelliMouse pointing device. Hold the SHIFT key down and rotate the wheel forward to lengthen the periodicity or back to shorten the periodicity. See Using the Microsoft IntelliMouse Pointing Device for more information on the Microsoft IntelliMouse pointing device.

Preston