La línea avance-descenso previene crashes

@McClellanOsc

There have been some retrospectives of the 1929 crash published this month, for the 90th anniversary. Here is what the NYSE's A-D Line looked like then, although no one knew about it because only Leonard Ayres and James Hughes were keeping the data:

And here is what the A-D Line looked like at the 1987 crash. Notice the big divergence:

Now here is what the NYSE A-D Line looks like currently. Notice the much stronger look than those two other episodes: