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I created a character sheet with one field named "ResPop" and another named Income and field source set to "ResPop.value * 2500" without the quotes. It works in the viewer fine.
In The Keep, I did the install character sheet reference and when I add a new character sheet, it gives me a typecast error on the Income field. The sheet works fine after I close the error though...
I don't know if I did something wrong with the character sheet, if it's a Keep anomaly/bug, or just me.