Chaldean numerology
Chaldean numerology uses a non-linear letter chart with values from 1 to 8. It is often used to study the name a person, business, or product is commonly known by. GetMyNumero currently focuses on this system.
Pythagorean numerology
Pythagorean numerology usually uses a simpler 1 through 9 sequence based on the alphabet's order. It is commonly used in modern numerology and often appears in full birth-name readings.
Why results differ
Because the letter charts differ, the same name can produce different totals and root numbers. That does not make one result automatically correct and the other wrong. They are different symbolic systems.
Which one should you use?
Use Chaldean when you want to test the spoken or public vibration of a name. Use Pythagorean when you are following a system that specifically asks for birth names and a 1 to 9 alphabet sequence.