An ambulatory blood pressure monitor is used to measure blood pressure readings throughout the course of a day. It is useful in diagnosing high blood pressure (hypertension) and can also be used to guide treatment.
The test involves fitting of a blood pressure cuff to the upper arm and this inflates automatically at intervals across a 24 hour period.
British Heart Foundation website
http://www.bhf.org.uk/publications/view_publication.aspx?ps=1000948
NICE guidance on hypertension