Substitutes are flag different from the alphabetical or numerical flag. They are used to enable the same signal flag either alphabetical flag or numerical pendant to be repeated one or more time in the same group. Incase only one set of flags is carried on board.
The first substitutes always repeats the upper most signal flag of that class of flag which immediately proceed the substitutes. Flags are hoisted this way.
The second substitutes always repeat the second and the 3rd substitutes repeat the third signal flag. Counting from the top of that class which immediately proceed then. No substitutes can ever be used more than once in the same group. The answering is to be disregarded a decimal point is to be this regarded in determining which substitutes to used.