Meaning of ひとつで自由に出せるように


The sentence is:

> ギャンブラーを名乗るなら、采の目ぐらい、投げ方ひとつで自由に出せるようになっておけ.

MC is revealing a secret how to win every dice game. But I'm not sure the
meaning of his words. Does it mean throwing dice one by one?




ひとつ（で） actually applies to the previous word 投げ方 here. It's kind of like だけ in
this usage; he is saying to become able to control the result of the dice
_solely through just_ the 投げ方 (way of throwing).

In the above sentence, the 投げ方 is described as the sole deciding factor for
producing the result.

Wiktionary has a good example of the usage:

> ある物事を左右する要素。 (The factor that influences another event.)  
>  君の返事 **一つで** どうにでもなることだ。 _(All it would take is) the right reply from you
> and this could all go away._

That's not to say that there aren't other ways the situation could be
resolved, but a reply would serve on its own to decide things all by itself.

大辞林 also highlights its use in this kind of situation.

> ひとつ【LHL】 【一つ】  
>  一  
>  （ 名 ）  
>  ⑥ そうすることによって決まる，それ次第であることを強調していうときに用いる。 「やるかやめるか決心 **ひとつ** だ」 「心の持ちよう
> **ひとつで** どうにでも変わる」 (used to emphasize that sth _will be resolved/settled by
> doing X_ ; or _hinges on / is dependent on X_ ). " _To do it or not -- it is
> all a matter of how you will make up your mind._ " " _You can be whatever
> person you want to be; it all depends on your attitude._ "

大辞泉 is more plain about it and says not much more than だけ, but I get the
impression that it's stronger than だけ and gives a greater sense of exclusion.

> ９ 名詞の下に付いて、それ以外にはないことを強調する語。…だけ。「身 **ひとつで** 脱出する」「母の手 **ひとつで**
> 育てられる」「行くか行かないかは自分の決心 **ひとつ** だ」 (Following a noun, emphasizes that there is
> nothing else than that. ... _dake_.) " _Make it out using nothing more than
> one's own body_ " " _Be raised solely by the hand of one's mother" "Whether
> to go or not entirely hinges on your own ability to decide_ "

(translations are mine)

