Full Idea
I can measure the length of something only if I know that it has not moved between the moment when I locate one end of it and the moment when I locate the other.
Clarification
When you reach the end, the beginning may have moved
Gist of Idea
Measuring space requires no movement while I do it
Source
Roger Scruton (Modern Philosophy:introduction and survey [1994], 25.3)
Book Reference
Scruton,Roger: 'Modern Philosophy: introduction and survey' [Sinclair-Stevenson 1994], p.360
A Reaction
A nice example of how even simple propositions have many presuppositions.