|Long pattern pieces and narrow long pattern pieces can be challenging to lay on the straight grain. The usual instruction is to measure from the selvage or fold to the end of the grain line, pin, then repeat on the other end. This can create problems because when you line up the second end of the grain line, the pin in the first end can twist and distort the fabric if the pattern wasn't laid out very close to the straight grain to start with.
I've been avoiding that problem by measuring the first end, putting something not very heavy (like an empty pin box) on the pattern at that end, then moving to the second end and measuring, then truing up the ends. It worked, but it's kind of tedious.
But tonight I had an aha! moment: I have two 18-inch transparent rulers. I placed them with their ends on the fold, one at each end of the grain line, then shifted the pattern piece under them until the measurements matched! They are heavy enough that they don't move around, but light enough that I can slide the pattern under them. Then I just pinned the pattern at the usual points (without bothering to pin the grain line because the rulers hold the pattern in place), and moved on to the next piece.