Off the Grid - Cipher Texts

I was playing around with Steve Gibsons' OTG and decided to design a way to cipher paper messages with it. Lately I have been getting into to paper based ciphers but most can be broken with ease. This is what I did, if you have any sugestions please let me.

To start I have generated a new grid for this example as it will be easier to follow along this way:

KEY:

Note: *This grid should NEVER be used for any real purpose as it is now public (but you should all know that)*

First step is to figure out what you want to cipher in this case it will be the phrase "Hi there".

No we have the plain text to encrypt we want to find a starting point - to keep it simple lets start in the first column (the symbol should be an '!').

All we do is find the first letter of our phrase ("H") in this column, once we find the letter we move over two (2) columns to the right to find the cipher text,

Next in the column where we got the cipher text (the "S" in this case) we look for the next letter.

Repeat until the entire plain text is ciphered.

To reverse this you have to go in reverse order. But how do you remember where the end point was? Notice the #9 at the end of the cipher text? That tells you what column you where in to find the last cipher text letter. Just move to left 2 columns from that symbol on the top and you are back to the last column.

Things to note:

You can make this way more complicated by shifting right and left or different number of times.

The same cipher text letter can be a different plain text letter. As you can see in the example the letter "m" is used three times but translates to three different letters in plain text depending on it's location. This defeats frequency analasis.

There is no "key" per se as the grid and column where you found the last cipher text letter are the key.

In theory this is uncrackable as long as the grid and last column remain unknown.

You could even exchange messages this way. Using a new grid for evey message and destroying it afterwords would render the plain text unrecoverable.

Let me know if I missed something here! Or let me know if you have any thoughts to make it better!