1. Get A Seismograph. Get a machine to measure ground shaking, a seismograph. There are several kinds. The seismograph that Charles Richter used to invent his scale in 1935 was one kind, adjusted one way.

2. Measure Distance to Epicenter. Richter worked in California, where earthquakes are shallow (less than 10 miles deep), and near (less than 350 miles from seismograph). Shaking from these quakes will arrive at your seismograph in a first and a second wave. The time between the two waves will tell the distance to the epicenter (point on earth above quake). Say that time is 45 seconds; your distance is 250 miles.

3. Measure Biggest Wave. To measure ground shaking, Richter's seismograph made marks on paper. He measured the biggest mark. Say your biggest mark is six inches.

4. Adjust Measured Wave to Standard Distance. Richter measured thousands of earthquakes, and made tables. So you can look up how big your six-inch mark would have been, if your seismograph were any distance from the epicenter. For his scale, Richter picked a standard distance, 100 kilometers. If your seismograph were that distance from the epicenter, then according to Richter's tables your mark would be not six inches, but 13 feet.

5. Read Quake "Size" on Richter Scale. One challenge for Richter was that small quakes made tiny seismograph marks, while large quakes made huge marks. So he invented a scale where every ten-times increase in the mark means moving up one whole number on the scale. Part of his scale looks like this:

Your mark, at the standard distance, was 13 feet. That is four meters, or 4,000 millimeters, or 6.6 on the Richter scale.

6. Understand Your Answer. You have measured an earthquake as a mark on paper. What does this mean? It means the "size" of the quake as a mark on paper.

But what people care about in an earthquake are damage, injury and death. These depend on: How near is the quake to a populated area? What type is the building? How closely is the area built and populated? What type is the ground? What direction is the underground movement?

What scientists care to measure in an earthquake are energy, force and increase in movement at the center true physical characteristics. Today's scientists hardly use the Richter scale. Even Richter meant it as only a rough convenience. He wrote:

``The idea of an earthquake magnitude scale based purely on instrumental records arose naturally out of experience familiar to working seismologists. ... A small shock perceptible in the Los Angeles metropolitan center will set the telephone at the Pasadena laboratory ringing steadily for half a day; while a major earthquake under some remote ocean passes unnoticed. ...

``To discriminate between large and small shocks on a basis more objective than personal judgement, a plan was hit upon which succeeded beyond expectation. ...''

About your 13-foot mark, it's theoretical. It's the mark Richter's machine would make 62 miles from Monday's epicenter, if the paper were big enough. Today's seismographs are paperless, digital, connected to computers. Scientists can program them to imitate Richter's seismograph, at 62 miles from an epicenter, so they can measure a quake on the Richter scale, for when journalists call.