To ensure that all data available in a historical archive is visually plotted, the Display Compression option consolidates the data point count (and reduces CPU loading) by dividing the plotting area of the chart into 200 time slices. In each time slice, a minimum, maximum, start, and end point for each section is retrieved from the database.
A maximum of 25,000 data points are visible on a graph. If two trend lines are defined, 12,500 data points are allocated to each.
The ASCII data point limit is 500 for each individual trend line. If this limit is exceeded, the following message appears:
Data that should be visible has been discarded because the time scale is too large.
The Display Compression option is enabled by default. If you zoom into a time span smaller than the duration of the calculated time slice, the visual representation may not be sufficient to examine the time span in which you are interested.
To ensure that the data presented is visually accurate after zooming into one-half of the starting time span or expanding out to twice the starting time span, Process History View re-polls for more precise data.
Whenever data is re-polled, the time range is reset so that zooming or expanding to half or twice the new time span will generate another data request. This approach guarantees that there is always a reasonable visual representation of data displayed.
To disable the Display Compression option, complete one of the following tasks: