Published in 1908 by The British Record Society this superb book is a list of the calendars of wills and administrations proved in the Court of the Archdeaconry of Exeter 1540-1799. (A calendar of wills is a list of wills arranged by year, and then alphabetical within each year, names and places of residence, and not the actual wills themselves.
Using this CD you can find the name that you are researching in the alphabetical index and then go to the page of the book that relates to that name. Here you can see if and when a will was proved for that person.
Remember that wills are an absolutely invaluable resource for genealogists as it is often possible to build up a very detailed picture of how the person lived by seeing what kind of items he or she passed on to relatives (and find out exactly which relatives were around at the time too!)