www.vriesendorp.nl, Octrooibureau Vriesendorp & Gaade B.V., visited on July 2nd 2010
vriesendorp.nl
Ir. C.M.R Davidson, BookletArchived 2011-07-24 at the Wayback Machine celebrating "One hundred years Octrooibureau Vriesendorp & Gaade", Published by Vriesendorp & Gaade in 1933
Ir. C.M.R Davidson, BookletArchived 2011-07-24 at the Wayback Machine celebrating "One hundred years Octrooibureau Vriesendorp & Gaade", Published by Vriesendorp & Gaade in 1933