Explain LVDT (or LVIT) Pre-Travel & Over-Travel

Two specifications often found on LVDT and LVIT position sensor data sheets are 'pre-travel' and 'over-travel'.  But what do they mean?  

- Pre-travel refers to the distance that the core (or target rod) can move before the intended measuring range begins.  In the pre-travel area, the LVDT's output may be non-linear or saturated.

- Over-travel refers to the distance that the core( or target rod) can move after the intended measuring range ends.  In the over-travel area, the LVDT's output may be non-linear or saturated.