With his own hand he copied manuscripts referring to Poland and Lithuania wherever he found them and in three years amassed a collection of one hundred and ten folio volumes. Where he was not allowed to copy he read and, on returning home in the evening, wrote out what his prodigious memory retained.
He meticulously compiled a collection of manuscripts about Poland and Lithuania through copying, which he amassed over a period of three years. In situations where copying was not allowed, he relied on his memory to recall the information and then recreated it by hand upon returning home each evening.