If you are measuring sea depth it doesn't make sense to have a minus sign when most of your values will be negative. Also, it is important to remember that sea

If you are measuring sea depth it doesn't make sense to have a minus sign when most of your values will be negative. Also, it is important to remember that sea level is an entirely arbitrary concept that depends on your frame of reference. On nautical charts elevations are usually measured against the lowest tide level which will be different to the datum on GPS (for example).