User Input Symbol

It would be great if there was an AVEVA supported (not custom) "User Input" symbol, for numeric data that could be referenced and used in other symbols' calculations. E.g. If the user puts 2 into the "User Input" text box, the calculation in a trend symbol is able to reference that and scale the data by that value. It would also be great to have a "User Input" symbol option for timestamp data, that could be used by the time functions in calculations in a similar way. I'm trying to build a Pi Vision screen our operators would use to optimize production by aligning a mass balance projection with a golden trend version, but our mass balance calculations discretely vary through time, i.e. I need to scale the data one way for the first period of time a different way for the second period of time (due to concentration changes), and the time frames are variable depending one things that happened with that batch.