Validate Textbox/Userform Number Range
 

I have one question which might be pretty simple to answer but so far I didn
't get it. I'm using a standard macro from MS in order to validate the entry
in a textbox of a userform. It looks like this:

Private Sub TextBox1_Change()

Dim okstop As Boolean
Dim Ok As Boolean
Dim mytext As String

okstop = False

Do
mytext = TextBox1.Value
If TextBox1.Value 1 And mytext < "" Then
TextBox1.Value = "" 'Clears the TextBox

'Shows a message box that informs you that you typed
'something other than a number.
MsgBox ("Percentage required, please type only numbers in
between 0 and 1")
Else
okstop = True 'You typed a number in the TextBox.

End If

'Continue with the loop if you click Yes.
'Stop the loop if they typed a number in the TextBox.
Loop Until (Ok = vbOK) Or (okstop = True)

End Sub

This works pretty fine as I wanted the user to enter only positive
percentages which means a number in between 0 and 1 (min 0%, max100%). Other
non-numeric letters should not be entered, that works as well. Now I would
like to change the code slightly so user can enter numbers in between -1 and
1 (min -100%, max+100%) and still not allow non numeric letters. Can anybody
tell me how this can be done, I was playing around but it never worked out.
Thanks a lot!

P.S. Sorry one more question, as I have around 30 textboxes in one userform
do i have to repeat this code for every single textbox or is there a way to
do the validation for all with one code only?