Definition of "usefull"

For Pens, so usefull for Scholars to note the remarkables they read, with an impression easily deleble without prejudice to the Book.

a. 1662 (date written), Thomas Fuller, The History of the Worthies of England, London: […] J[ohn] G[rismond,] W[illiam] L[eybourne] and W[illiam] G[odbid], published 1662