Sentence:  When the two bodies are in close proximity, the gravitational field is stronger, the passage of time is slowed– and the time between pulses (or ticks) is lengthened. Then as the <WSD>pulsar clock</WSD> travels more slowly through the weakest part of.the field it regains time. 
Meaning of the word marked with <WSD> tags:  The regular timing of pulses from a pulsar.