Looking at the next page of the entry which shows figures, worked out that the entry for Digory refers to Articles of agreement, over 5 years figure quoted is £65 with £3 5s. duty. So perhaps that makes more sense? Its not an apprenticeship as we would know, or was typical at the time.
Rather than go to Kew might be worth a subscription to Ancestry, or if you are a member of your local library see if they have access for free, many do at the moment. You do need a pin number for your online link to your library.
Hope this has helped Good luck