Originally Posted by LindaMRB

I think what you meant is a compass. I have one that can old a pencil - well worth the purchase price. There might be a clever way to attach the soap sliver using some clips… to avoid slippage and just a tedious process.
I've used soap before to mark a quilt but the problem has been that it can rub off before you get there. It's just as well you marked it after doing the inside.
Please post the finished quilt!