AD7124-4 FS Setting in Virtual Eval Tool


When I try to set FS = 1 in Virtual Eval Tool for AD7124-4 I get following error: "Fs of 1 is outside range for the AD7124. The Fs for the conditions selected must be between: 4 and 2047. Please enter a valid Fs." But AD7124-4 datasheet says that FS = 1 is possible value.

I would appreciate it if you could comment it.