Question

A worker in an office 1350 m from The Big Ben sets his watch to 1 o clock when he hears the clock chime through an open window . An hour later at 2& clock he checks his watch using the chimes of the Big Ben heard from the radio and finds that his watch is 4 seconds slow. The watch is working correctly.

Explain why he had set his watch 4 seconds slow at 1 o'clock