The Chaldeans were ancient people who ruled Babylonia from 625–539 BC. Therefore, this system is also known as the Babylonian numerology system. The basis of Chaldean Numerology is that each letter has a unique vibration and is assigned a number from 1 to 8 based on its energetic quality. It recognizes the energy changes that occur when you or someone else speaks or thinks. The sound of someone speaking comes out in vibrations of different frequencies that affect the speaker and those around them. In this type of Numerology, the single digits reveal the outer nature of a person, while double digits describe inner qualities of a person. The Chaldean system uses the numbers 1-8. The number 9 is not used in the system because it is regarded as sacred due to its connection to infinity. The number 9 was sacred not only because it was symbolic of the highest level of spiritual attainment, but also because its level of creative energy was higher than all other numbers. It is however possible for the number 9 to be the end result in these numerology calculations.