When I change between pages (using the template menu from IA), I have two pages each with its own power chart in a flex container. For about 3 seconds I get a message at the bottom as per thread title.
I have 3 tags on one chart, and one tag on the other. Default settings, realtime last 8 hours.
1 Tag on a chart is ~500(i think this is configurable) values to render the line from historical data.
If that tag has more than the requested amount of values for the time period on the chart, it Aggregates the data to provide the right amount of values to render.
This request is processed on the database, then sent to the gateway, which sends the data to the perspective session you are viewing it on, then the local browser has to render the graphics using its rendering engine. This takes time, and depending on load on various parts of that chain, it takes longer or shorter times.