The Koch house system, sometimes called the “Birthplace System,” emerged in the mid-20th century through the work of Friedrich Zanzinger, Walter Koch, and Heinz Specht. Koch treated the Midheaven as the chart’s main time reference, since it is determined directly by local sidereal time, and built his house system from successive permutations of the M.C. marker.
Although often compared to Placidus, Koch divides time differently. Rather than solving semi-arcs directly, Koch begins with the Midheaven degree and calculates how long that degree would take, in sidereal time, to travel from rising to culmination at the observer’s latitude. This interval is called the diurnal semi-arc (DSA), and it is divided into three equal parts. In this sense Koch is similar to Alcabitius. But here is where it differs:
Having determined the DSA, the sidereal time is then advanced successively by one-third of this interval, and for each new sidereal time an imaginary ascendant is calculated. These successive hypothetical ascendants become the intermediate house cusps.
Koch’s calculations depend on geographical longitude, local sidereal time, latitude, and the way the Midheaven degree rises. For this reason, Walter Koch described the system as being calculated “for the exact birthplace.” However, most quadrant house systems also depend on local sidereal conditions, so they too are location-specific.
Like Placidus, Koch produces unequal houses. It became especially popular in continental Europe among psychological and humanistic astrologers in the mid-to-late 20th century. Its later decline seems to be due to changing astrological fashions, along with the growing dominance of Placidus in English-speaking astrology.