http://www.futuredekho.com/kaal-sarp-yog-remedies,A horoscope is said to be afflicted by Kaalsarpyog, if all the seven planets come between rahu and ketu. Rahu is taken as serpent's head and ketu as dragon's tail. Kalsarp yoga is considered as a evil for a horoscope as all the good planets coming in between lose their positivity to an extent which makes a person go through problems, losses, ill health etc. When only half of the chart is occupied by all the planets, then we say complete Kaalsarpyog yoga is formed. However, even if one of the planet is outside the Rahu Ketu Axis then we do not consider it as Kaalsarpyog.