I am in a situation where I need to display a barcode of 18 alphanumeric characters. In case the barcode scanner is broken or cannot read for any reason, the operator will have to manually type in that code. Hence I'd like to present the code in the easiest way for the operator to read the bits while he's typing.
My experience says that groups of 3 to five characters are good for that purpose, and having all the groups with the same length is also desired. Just like credit cards: 4444 5555 6666 7777 looks so easy on the eyes.
But I've got 18 characters. 3 groups of 6 feels that each group is too lengthy. 6 groups of 3 feels too many groups.
I could make 3 groups of 5 and one of 3. But in this case, the smaller one should come first or last?
What other suggestions do you have?
Update: here's an example of the code while I was testing the 5-5-5-3 pattern