How To Make Sure That User Input Is Numeric

I am writing a small program here and this i=code is straight out a book and it doesn't seem to work. Its supposed to ensure that the users input is numeric and not contain letters.

Module Module1
Sub Main()
Dim user_Input As Single
Dim H As Single
Do
Console.Write("Enter you'r Height in Meters: ")
user_Input = Console.ReadLine
Loop Until IsNumeric(user_Input)
H = CSng(user_Input)
Console.WriteLine("You are {0} meters tall", H)
End Sub
End Module