What are the differences between the Richter Scale and the Mercalli Intensity Scale

the mercalli scale measures the effects of an earthquake from 1-12. 1 means very few people can feel it, while 2 means cars rock slightly. 12 is total destruction there is no instruments or measurements, just based on observation. since it is based on observation, people may say that an earthquake was a 3, while others say it is a 4 or 5

richter scale measures the amplitude of a wave using a seismograph, on a log scale of 1-10. it is more of an exact measurement