To create a grey step-wedge in Photoshop:

• open a new file in greyscale mode;
• set the canvas size to approximately 6" x 4" format at 300 dpi;
• fill the background with 100% black with white as the foreground colour;
• select the gradation tool to create a linear gradient (foreground to background) with opacity 100% in normal mode;
• click at one end of the image and drag the cursor to the other end of the frame;
• using the rectangular marquee tool, draw out a rectangle to define the dimensions of the step wedge, being sure to include the whole range of the gradient;
• select image - adjust - posterize to break the gradient in to steps;
• enter 21 as the posterization value and click OK - this creates a step-wedge from 0% to 100% in 5% increments;
• a step-wedge in 10% increments can be created by using a posterization value of 11;
• the value of each step in the wedge can be checked using the eyedropper tool and the show info window;
• label each value on the wedge with the type tool; and
• flatten the image and save.