There is another way of doing polyalpebetic ciphers. It may be the same idea though.

You have a key word KEY and the message Break this cipher

you arrange the tables according to the keyword and a regular alphabet

KLMNOPQRSTUVWXYZABCDEFGHIJ
EFGHIJKLMNOPQRSTUVWXYZABCD
YZABCDEFGHIJKLMNOPQRSTUVWX
ABCDEFGHIJKLMNOPQRSTUVWXYZ and then take your message

BREAK THIS CIPHER

You encrypt by taking the first line with the first letter (B becomes L) the second letter with the second line (R becomes V), third with the third line, fourth with the first line and so on. Decryption is done in the opposite direction.

The weakness with the fequency count. You know how often E is used usually in the english language T is used some perecent of the time. You take every other letter in the count and keep trying different key lengths until you get "E" to come out the most, "T" the second most and so on until the fequency count looks like a monoalphebic cipher. This type of nondigital encryption is effective with short messages. The longer the message the better the possibility of breaking it.

There are other techniques that you can use to obscure it, like reversing alphabets, adding null characters, and using longer words or changing keywords several times through the message depending whether you need a speedy decryption or strong security.

Breaking it is tedious but possible. Remember that the cipher should be at least strong enough to keep the information secret for as long as the info is valuable.