Graph function dialog box, "edit as table" will not work if the x-axis does not start at zero.

The obvious work around is to edit the graph graphically - click on the graph to move the graph line.

The value for the point being dragged can also be tweaked by entering values in the "current position" "y" edit box.

Another work around would be to adjust the x-axis to start from 0, so if the input rangej should be 1.0 to 1.5 you would make the x-axis go from 0.0 to 0.5 then you could  "edit as table" and adjust the expression for resulting variable to work with the shifted graph, e.g. "evapo multiplier from specific gravity" = graph(specific_gravity-1.0).