為甚麼地鐡的八達通接收器在右則，而轉盤在左則？

正確。八達通接收器和插票孔都設在用者的右手邊，這是方便大多數慣用右手的普遍人。
通常入出閘機的轉盤都同設於該八達通接收器那邊 i.e.右邊。如發覺有入出閘機的轉盤設在左側，那應該是該入出閘機可以提供雙向的出入閘，而剛好這部入出閘機被set成與原來設計的進出方向相反。
地鐡的轉盤式入出閘機的設計是即使可以雙向使用，但每次只提供一種方向。而九廣東鐡舊式轉盤式入出閘機，有部份在提供雙向使用時，兩個方向的乘客均可使用。

右手必八達通
左手推閘

根本就無答到問題

In most cases, the turnstile is attached to the same machine you scan your Octopus card. For the one you saw with the turnstile attached to the machine to your left, that means those machines are two-way.

For MTR, those machines + turnstiles can only operate one direction at a time. You can see some of this kind of two-way machines in Lok Fu Station.

For KCR, those two-way machines also exist with similar operations. But I saw in KCR stations, those two-way machines + turnstiles can operate both directions at the same time.