I CHING: DIVINATION WITH ONE COIN:
This is a preferred way.
A single penny is thrown three times to determine each line. (A coin can be spun instead of throwing or flipping). (Heads are 2, tails are 3.) The results of the three tosses are added together.
Then it is thrown three more time to determine the second line,
And so on.
The single coin is thrown eighteen times in all for one hexagram.
The advantage of this system is that it allows for the maximum possibility of chance.
When throwing three coins at the same time, they often stick together within your hands and come out the same as the time before. This limits the total possible options for the coins and could be considered as biasing the outcome.
Throwing one coin at a time removes this limitation and keeps a maximum amount of possibilities open. Unfettered randomness is achieved.