Raster Calculator- Making variable from paramater

[KevaHackshaw]

I am trying to make the raster calculator expression a variable (Make variable> from parameter) but the option is greyed out. Does anyone know why this is happening and how do I solve or get around it? I do not have this problem with any of other tools in the model. [ATTACH=CONFIG]14756[/ATTACH]

[SimonFraval]

Any ideas on this? The only thing I can think of to make it easily editable is to export as a python script. Making a variable from raster calculator would be more convenient though.