SubSurface Instruments LD-18 Operation Manual page 27

<NR system>
This function permits reduction of transient undesired noise that lacks continuity. High effect is obtained
when the set level is elevated. There is a certain time-lag (silent time) in the NR mode before sound is
heard through the headphone since the sound hearing switch was pressed.
Lv.1 : 0.2second
Lv.2 : 1.0second
Lv.3 : 3.0second
* Precautions for use of NR system
Positively place the pick-up sensor on the ground before pressing the sound hearing switch. If sound hearing
is performed in the state where the pick-up sensor is floating, accurate result cannot be obtained in either
sound volume or minimum level value.
<SENS switching>
Switching out of the range of 00~40 is permitted. The sensitivity of this detector changes in correspondence
to the set numerical value.The magnitude of the sound heard out of the headphone also changes accordingly.
The MIN value, however, is not linked to switching of SENS.
<Forced motion OFF>
When the battery voltage becomes less than a certain reference voltage, the motion of this detector is forcibly
shutdown for protection of batteries against over-discharge. The screen on the liquid crystal display disappears
in this case. Replace batteries with new ones.
<Main unit's alternate ON / OFF switch>
Use this switch in case optional pick-up sensor dedicated to valve/tap sound is used. This switch is push lock
type, so it doesn't need to hold down the push button. When the lock switch is ON, the sound is suddenly
outputted after main unit start up. Be careful at the time of the sensor use of main unit's switch.
6. Method for water leak detection
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[Hardware]