In fact, Beckmann's account, and thus Mackay's by derivation, was primarily sourced to three anonymous pamphlets published in 1637 with an anti-speculative agenda.
Tegelikult tugines Beckmann (ja seetõttu ka Mackay) peamiselt 1637. aastal avaldatud kolmele anonüümsele spekulatsioonivastasele pamfletile.