Presys PC-507-IS Technical Manual page 47

The value of Output High must always be higher than Output Low.
Input High and Input Low parameters must never be equal. Thus, any type of direct
or reverse retransmission from input to output can be obtained.
Scale and Conv functions may be disabled by selecting the NO option
and pressing ENTER, as shown below:
Fig. 26 – CONV Function
SCALE CONV
 NO
Page 46