What is tile gauge??

[stuartturbo]

Numpty question
weekends task is cladding dormer( providing i finish building it )
but what is gauge.
114mm for the tiles but is gauge
Center to center distance on the batten ( seem the way to me) Or
top to bottom off batten as some diagrams seem to show

 

[palaceray]

For tiles the gauge is measured from top to top of battens, for slates bottom to bottom.