Tile efficiency works just okay for one's own hand, but what about the tiles that flow out? Obviously, you shouldn't call every single one of them, but that doesn't mean you should ignore them either. How to judge? What to consider when calling? Well, the basics are sumed up in the following text.

From: http://beginners.biz/n_02.html

Basic judgement for calling tiles

Based on what we learnt last time, to call a tile? to not call a tile? let's think about that judgement.

Ex1

2m4m5m7m4p8p1s2s6s8s9s7z7z Comes out: 7z Dora: 3p

East one, No-Dealer and you have a hand like ex1. In the third discard 7z came out.
Call this tile?

Let's see the merits and demerits.

◆Merit
You secure 1 fan, so it gets easier to win.

◆Demerit
Defense power falls.
It will only be worth about 1000-2000 points.

To call or not to call,
comparing the merits and demerits of calling, judge which one is bigger.

Picture a scale like the next one:

scales1

If the the scales were tilted towards the left: call; if the scales were tilted towards the right, then don't call.
The important thing here is that the relative weight of these values, changes according to the situation.
Judgements like "There are more merits than demerits" cannot just simply be made that easily.

Let's give it another small analysis.

2m4m5m7m4p8p1s2s6s8s9s7z7z Comes out: 7z Dora: 3p

Speed:Certainly having 1 fan secured it becomes easier to win but、since it has bad shape even if you call there is a high chance you won't win. ⇒ The "speed" merit is of low value.

Defensive Power:If you want to win this hand there is a high chance you'll have to call more tiles, and the your tenpai will come really slowly, so it's extremely dangerous. Now we are not holding even one dora. ⇒ Defensive Power Down's demerit is huge.
Point Gain:There is a high chance for 1000 points、but even menzen this is a cheap hand ⇒ Point Gain Down's demerit is relatively low, but the value is cheap.

Afterwards you have to consider what go-around this is, and whether you're dealer or not, East round or not, but
it will mainly become like the next image:

scales2

The scales are tilted towards the right. This means, it's better not to call.

Ex2

2m2m4m6m7m7m2p3p4p5s7s8s8s Comes out: 6s Dora: 7s

East 1, you're dealer, you are on second place with a 2000 points possitive, and it' the sixth turn,

let's suppose the person to your left has discarded6s .

Speed:Drastically up. Even if you get to a concealed tenpai, 6s is a difficult wait to win on.

Defensive Power:Even if we call all tiles, we'll be ready with just two calls. Furthermore、since it's only middle tiles in this hand the Defensive Power is weak even concealed.

Point Gain:With menzen riichi it will be 7700 or more, so it's greatly reduced.

scales3

If you win as dealer you can continue, therefore the merits to call this tile are higher.
It is clear that it is better to call.

Like this, thinking about the merits and demerits of calling,
all situational judgements become basic.

People who are strong at mahjong, have these scales very well calibrated and balanced and are therefore strong.
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PS: Yeah, they were scales and not equations in the original text, but I sure as hell ain't drawing and uploading scales at 1 AM. Text form will do. Aaaand, I'm also working on an other translation project right now too involving puyo's blog. Check RM tomorrow and you'll see what I mean. Anyhow, until next time~ I'll probably will touch the subject of KAN.

EDIT: Now they -are- scales~ Thanks, Osamu~