Actually the "correct" defaults as put forth by MACD creator Gerald Appel are 12-25-9 and 8-17-9. The latter gets invariably ignored and the former gets invariably typoed into 12-26-9. I figure this must have been first typoed in Edwards & Magee or some other TA "bible" for the error to be so widespread.
Appel himself has surrendered to this typo as I saw him use it in a recent (aka this century) article when discussing his brainchild. This indicates either a man with no self-respect or a man who knew he was selling bullshit from the start.
Really, I am a student of how financial indicators came about but I have never seen this story...I would like to read this article that you describe.
Why don't you post a link so we can all enjoy it?
Whenever you see me make an assertion about another's work or a discussion on the work, I will back it up with reference....I am sure that you will agree that this is only fair
this link shows a PDF file titled
Construction and Application of MACD Indicator by George
Appel
http://broadcast.ino.com/workshops/INLV07GA/workshop.pdf?lt
Shows that Mr. Appel was not stuck on a particular indicator...he actually discusses various applications and parameter settings.
another interesting discussion on MACD is here
http://www.systemsandforecasts.com/pdfs/MACD.pdf
I might not use all of it but it is still worth reading for ideas.
I would not be surprised that the 26 day EMA parameter was an outgrowth of the standard 200, 100, 50, 20 day averages. So dividing 50 by 2 you get 25 ....but you need a starting point to calculate such an exponential moving average so that would mean you would need 26 days
I might have left the impression that MACD was useless as I did not believe in using a signal line...but I do trend the MACD lines and that is also done by users.
Where I have (I believe) a unique idea is tying MACD together with Bollinger Bands and BBwidth indicator...that is MY creation and it works...it works even better with one more indicator
To call Mr. Appel's work and promotion wrt the MACD concept BS is ridiculous....his work has stood the test of time.
Just what have you contributed to the body of Technical Analysis??? I wonder...