Sinusoidal systems of house division are similar to Porphyry houses except that instead of each quadrant being divided into three equal sized houses, the middle house in each quadrant is compressed or expanded based on whether the quadrant covers less than or greater than 90 degrees. In other words, houses are smooth around the zodiac with the difference or ratio in quadrant sizes being spread in a continuous sinusoidal manner from expanded to compressed houses. Sinusoidal houses were invented and first published by Walter Pullen in his astrology program Astrolog in 1994.