Here are my calculations:
Piece A is a square approximately 6 3/16 in. This patch is on-point so if you are using a print that has an image or directional pattern on it you will have to decide whether you want the image/pattern to be tilted, or if you want all four sides to be cut on the bias.
Piece B is a square approximately 2 7/8 in. cut in half diagonally. Additionally, I like to trim the acute corners with cuts perpendicular to the hypotenuse such that the hypotenuse is 2 1/2 inches - this makes it easier to line up the patches win piecing.
Piece C is a trapezoid cut to the dimensions described above. I tried two ways to rotary cut this piece:
The Hard Way (cut first) - Cut a strip 1 15/16 in. thick and 6 7/8 in. long. Cut off the corners at 45 degrees, and verify that the top measures 3 1/16 when this is done. This leaves the short sides of the trapezoid (the sides that will ultimately be the edges of the block) on bias, but I thought it was better to have the long seams on grain. If you prefer the edge seams to be on grain (or if your printed image/pattern requires it), you can start with a 4 7/8 inch square and cut diagonally into half triangles, then make a cut parallel to the hypotenuse 1 15/16 inches wide.
The Easy Way (sew first) - Cut the 1 15/16 in. strip the same length as the Piece A (6 3/16 in.).
Sew four of these patches to the Piece A and press the seams open. Then rotary cut at 1/4 inch from the corner (making sure to keep the top and bottom points for the square lined up with your ruler).
What Not To Do:
I don't know how I got this far before I realized I was doing it wrong!
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