Read the Directions!
I will preface this post by saying that I am not a fan of specialty rulers, especially those that are good for only one task, and most especially those that work for a limited size of block. I make an exception for those made by Deb Tucker/Studio 180 Designs because of their versatility.
I think I mentioned earlier that I "cheated" on Jenn's Journey by using some already-made snail's trail blocks.
However, this decision also affected the dimensions of the diamonds and square-in-a-square blocks (versus what was in the pattern). I thought I was smart enough to figure out what I needed to do. That was my first mistake! The second was not making any notes on what I was planning to do and letting it sit in a box for over a year. 😕
In the project box I found Deb Tucker's Diamond Rects ruler which I used to establish the odd angle for cutting the diamonds. But I didn't notice that the ruler also included measurements for cutting the corners. Instead I used the corners I found in the box. As a result, my Diamond blocks were coming out 1/8"too narrow. I was able to compensate for that in the seams.
Then I spent hours trying to figure out how big to cut the center square for the square-in-a-square blocks. I had gone through this same exercise just a few weeks ago when I was working on Everlasting! (shown below).
Well, duh! I have Deb Tucker's Square Squared ruler hanging on the ruler board! It tells me to cut the center squares from a 3-1/2" strip.
So I cut 3-1/2" squares. And I'm thinking why would anyone need a template to cut a square?
The ruler also told me how big to cut the corners.
Which I dutifully followed. But my SiaS was too big and the points would be cut off ... because the square which I cut from a 3-1/2" strip would have been 3-3/8" if I had used the ruler template!
Just so you know -- I know how to cut 3/8" but I understand not everyone has a ruler with eighth-inch markings so I'm not making a negative comment about the ruler. I obviously did not read the instructions!