# Mask Test Requires Color Grade or Gray Scale Persistence

Mask tests require a pixel-hit database that consists of all displayed data samples. Every time a display sample point is acquired on a display coordinate (pixel), the counter for that coordinate is incremented. The maximum count for each counter is 232. The pixel-hit database continues to build until the instrument stops acquiring data.

To reset the pixel-hit database, click Clear on the menu bar. Changing a channel's vertical scale, vertical offset, horizontal position, horizontal scale, and filter status (on or off), trigger settings, or performing an Auto Scale will also reset the pixel-hit database.

The pixel-hit database is active when the color grade or gray scale persistence display setting is used for a real-time eye (with overlaid Unit Intervals) or regular time-domain waveform (with overlaid acquisitions). (Histograms use a similar database where hits within vertical or horizontal slices, or bins, are recorded.)

The following events do not reset the pixel-hit database:

- Using Stop/Single acquisition (Stop/Single on the menu bar)
- Using Run acquisition (Run on the menu bar)
- Loading a new mask
- Starting a new mask test
- Turning on mask margins
- Changing mask margins
- Scaling the mask
- Executing eye diagram measurements
- Performing a histogram measurement