Answer
Commentary
Criteria of backing to one before for ready
If you discard 5m, this hand is ready.
And if you call Riichi, this hand has Mangan ; riichi, All simples, double sequence, and dora, it's not bad.
Statistically, you may call riichi.
But this Kanchan is too difficult to win experimentally.
Many player wants to back to one before for ready.
When would you be allowed to retrogress??
One criteria is
"Back to one before for ready if there are more than six tiles of valid alternatives"
Why 6??
The probability of drawing the desired tile in one round is approximately 3% (1/34).
If there are 6 types, that's about 20% per one drawing.
There's a good chance you'll get one of these tiles within 5 rounds (20×5=100)
If it takes longer than five rounds, it's better not to wait in most cases.
In this hand, 1m, 4m, 7m, 4s, 5s, 7s, 8s, is valid to wait Ryanmen.
If you draw Souzu, you can wait triple sided, and look to triple sequences of 4 5 6.
You should back in such a case.
-------------------------------------------------------
This Shochu (Japanese liquor similar to vodka) is aging with the sound of Mozart.
Sound Ripenin is that means.
I don't know the reason, but the The frequency of Mozart's music is said to be the most mellow.
In fact, it's pretty good.