Brian;

> The way I'd encode this for a database is to have the program ask for two magnitudes, one for the lower bound and one for the upper bound.

Agreed.

> If either one is left blank or made zero (blank would convert to zero internally) it would be assumed as open ended.

That's a problem for me. TrueBasic doesn't allow missing values in an input statement.

> For example:
3.5 6.8 - This is a specific range with lower and upper bounds
0.0 6.8 - This means any quake magnitude up to and including 6.8
3.5 0.0 - This means any quake magnitude 3.5 and above
0.0 0.0 - This should not be accepted and request correction from the user

The problem is that zero means zero, so 3.5 0.0 would cause an error. The upper end can't be smaller than the lower end.

> HOWEVER!!! (there's always a however) What about negative magnitude quakes? I mean, there is such a thing as a mag zero or even negative magnitude quake. I've seen a few in the catalogs.

Correct but why would anyone predict such small events?

> But, I think it's safe to discard this tiny technicality and presume 0.0 is the bottom end.

Actually the bottom end depends on the catalog and the upper end depends on the scale.

> Other thoughts: x.x is sufficient accuracy; if input is single digit assume x.0; all these rules should be fully documented, perhaps with pop up help boxes?

By all means.

> Magnitude scale? I agree that a magnitude scale should NOT be given.

> But which scale is used for testing? Although this is not an issue for the database that we're helping Michael with, you may want to consider the following idea, Roger, for your evaluations.

> Obviously if there is only one mag available, that's the one to use. But what if there's more than one? I think you've said you use the highest of any available?

Yes. Avoids a lot of arguments and people are generally after the big ones anyway.

> That's one idea. But are not some magnitudes "more correct" than others? Perhaps a ranking of correctness can be determined and in the case of multiple magnitudes, the most correct is chosen?

That's one possibility if you could get seismologists to agree on the ranking.

Roger