Be aware of the pitfalls with creating waves on the fly with {}

[t-b]

Function Callit()
    variable var

	GetData({var})
End

Function GetData(WAVE data)

End

creates a SP wave. The WAVE type of the argument in GetData determines the created wave type. So use WAVE/D if you always need DP waves. Or introduce WaveDouble, see AllenInstitute/MIES#2697. Doing WAVE/T forces a text wave as parameter.