If the assumptions used in calculating energy are changed, then this seriously affects the final result, even though the same body of data might be used.

If one introduces the concept of energy of an earthquake then that is a theoretically derived quantity.

I suggested that we might compare earthquakes in terms of the measured amplitudes recorded at these stations, with an appropriate correction for distance.

My amateur interest in astronomy brought out the term 'magnitude', which is used for the brightness of a star.

By moving them vertically, a representative mean curve could be formed, and individual events were then characterized by individual logarithmic differences from the standard curve.

For example, some stars put out large amounts of energy in the infrared part of the spectrum, so that this can produce a different relative magnitude rating than using light energy from the middle of the spectrum.