Can't you use MouseX() and MouseY() instead?
Example:
OLDMX=0 : OLDMY=0
NEWMX=OLDMX : NEWMY=OLDMY
Repeat
MOUSE=MouseClick()
NEWMX=MouseX() : NEWMY=MouseY()
If NEWMX<>OLDMX
Rem Delete old text by writing over it in black
Ink RGB(0,0,0),RGB(0,0,0)
Set Cursor 0,0 : Print "NEWMX = ";OLDMX
Rem Now update the text in white
Ink RGB(255,255,255),RGB(0,0,0)
Set Cursor 0,0 : Print "NEWMX = ";NEWMX
OLDMX=NEWMX
EndIf
If NEWMY<>OLDMY
Rem Delete old text by writing over it in black
Ink RGB(0,0,0),RGB(0,0,0)
Set Cursor 120,0 : Print "NEWMX = ";OLDMY
Rem Now update the text in white
Ink RGB(255,255,255),RGB(0,0,0)
Set Cursor 120,0 : Print "NEWMX = ";NEWMY
OLDMY=NEWMY
EndIf
Until MOUSE>0 or (Scancode()=1 or Scancode()=28)