There is a science common to geometry and arithmetic which considers quantity generally as measurable.In more detail he states:-Surely there is a certain science common to arithmetic and geometry to which properties common to all quantities pertain: since a proportion is common to all quantities, not only abstract ones such as numbers and magnitudes, but also concrete ones such as times, sounds, voices, places, motions, and forces (for all these and many others are said to have a proportion if their relation is considered from the viewpoint of quantity).Van Roomen proposes unifying geometry and arithmetic under his concept of 'mathesis universalis'. The importance of these ideas must be their influence on Descartes' use of algebra for geometric problems. The third part of van Roomen's 1597 work, consisting of ten dialogues, points out the errors in Scaliger's attempt to square the circle and also points out the errors in the works of several other mathematicians including Oronce Fine who had made similar claims.