Meridian

Physical unit
Unit name	Meridian
Unit symbol	${\displaystyle \mathrm {mtr} }$
Physical quantity (s)	length
Formula symbol	${\displaystyle l}$
dimension	${\displaystyle {\mathsf {L}}}$
In SI units	${\displaystyle 1\,\mathrm {mtr} =0{,}51{\overline {4}}\;\mathrm {m} }$
Named after	Latin pars minuta tertia , "part reduced for the third time"
Derived from	Meridian second

A meridian tide [ mtr ] is the 60th part of a meridian second (arc second ), i.e. 0.5144 m.

The name is derived from the tertiary of the angular dimension as a further subdivision of the angular degree (60 tertiary = 1 second), definition:

The meridian is the 3600th part of the nautical mile or nautical mile

${\displaystyle 1\;\mathrm {mtr} ={\frac {1852}{3600}}\,\mathrm {m} =0{,}51{\overline {4}}\,\mathrm {m} }$

Rounded to 0.5 m, it is often used for the railing log to determine the speed of a boat through the water. 1 meridian is the distance that a ship traveling at 1 nm / h = 1  knot covers in one second , namely the 3600th part of a nautical mile ( meridian minute ).