HIstorical trending of discrete tags

Ignition 7.8.5

I’m trying to show a plot with an Easy Chart of some discrete tags that are stored only on change. Using the Raw resolution mode, I get short chunks of lines, as the line doesn’t plot if the previous stored value happened prior to the plot start. As an extreme example, if I look at a plot where none of the values changed during that time period, there will be no lines on the plot at all.

However, if I use Fixed resolution mode, the Easy Chart interpolates the data and shows data where it should not be. For example, a discrete bit that was off for a long time but turns on during the plot window will be shown as having always been on, based on the aggregation mode in the pen definition. I can change it to Average from min/max and it will show a slope up to the on data point, but that’s not really correct either.

I’ve looked through the docs but none of the other aggregation modes seem to be what I’m after. Closest Value is kinda similar, but what I’m after is probably more like Previous Value; in other words, I want to plot the last known value until another value is logged. This seems like a pretty common use case but I can’t seem to figure out how to do it… I’d prefer not to force the database to store a bunch of tags whether or not they change, as that seems like a silly waste of disk space.

You’re struggling because there’s no good answer. What you wish to plot are really events, and the only accurate way for a pen to represent them is with the square-edge transition shown at the actual timestamp.
I created the NoteChart module specifically for this situation, where it isn’t practical to show pens for all of the booleans whose transitions might be significant, but it is practical to show stroke marks on a chart with event names/descriptions.