Trending using variables for minimum and maximum.
In order for variable values to take effect the page to be processed has to be refreshed this works fine when the read is cyclic but when permanent read is selected there isn't a way to refresh the page to be processed to accept the new values.

XBTL1000
Trending
Min
Max
Variables

This is not an issue, but it's the principle of XBTL1000 way of working :
When the permanent read is selected in the properties of the curve, the XBT is always plotting even if the page is not displayed. This is why the terminal reads the max and min variables only when booting up, to keep in memory the all plotting. The only way to update the max and min is to turn off and on the terminal.
This might not be the best way , but we will register this request as a future enhancement for the next version. In the mean time, a corrective action will be carried out in order to explain clearly this point in the user's manual.