Exhaling one unit of time, inhaling one unit of time ,and retaining breath for four units purifies the channels through which breath flows.—-Maharishi Ramana.
Comment; The method of Maharishi Ramana is of self-inquiry. And he mostly told and gave his instructions for observation of the mind. And if thoughts starts, he said, ask questions to yourself,” To whom these thoughts arise”? And your answer will be,” To me”. Then ask yourself,” who am I?” by repeating this process, the thoughts will get destroyed and finally you will touch the bliss.
But here maharishi is telling about Pranayam. it is clear that one unit of time for exhaling and one is from inhaling. And four unit time retaining the breath (breath should stay inside). This method will purify the channels through which breath flows. This is a method of Pranayam is for those who cannot able to do self-inquiry and Vippasana. (Observation of breath).