You can also use the extension NO INTERVALS so that if you are not using the HIGH value, you can hide it.
e.g.
data: matnr type matnr.
select-options : p_matnr for matnr default '123' no intervals.
at selection-screen output.
loop at screen.
if screen-name = 'P_MATNR-LOW' or
screen-name = 'P_MATNR-HIGH'.
screen-input = '0'.
modify screen.
endif.
endloop.
