Tractatus Astronomica, Cambridge University Library Ms li.3.3 fo. 15v-16r.
, depicting a hand that at first glance appears to have six fingers, shows the method of using the fingers for reckoning or computus as recorded and promoted by the Venerable Bede
"Such mnemonic and cognitive techniques retained their vitality and importance into the early modern period, coexisting with new devices for retrieving and remembering knowledge, such as the commonplace book. People continued to rely upon their hands to remember information of all kinds, including religious and moral precepts" (https://exhibitions.lib.cam.ac.uk/reformation/artifacts/a-medieval-hand-mnemonic-for-reckoning-time/, accessed 10-2020).