Calibrating a new depth sounder

If you are replacing another sounder then no calibration should be necessary.

You are not normally calibrating sounders anyway, you are simply adjusting "offset" to account for position of the sounder compared to surface of the water.

If you want the sounder to show actual water depth then you have a + offset in the settings which for   typical 36 foot yacht might be +0.3-0.4m. 

I assume you know the draft of you vessel from specifications. Set the alarm on the depth instrument to be significantly higher than your vessel draft.

Some people set a negative offset so that the depth measurement corresponds to "below keel" depth. I think the majority of sailors don't agree with that approach for a number of reason. Primarily they want to know real depth to compare to charts,  tide levels and fir anchoring calculations.

Set mine to show 1m less depth than there is. I know there is a tiny bit more clearance ... but my crew don't!