Save this image and print it out at the size you'd like to draw the horse. You can trace the line drawing to give your drawing a quick start and you can refer to the value notations as you work through the lesson.
Graduated Grayscale
I'll be referring to a "graduated" gray scale with numbers from one to ten in my instructions. "One" is the white of your paper and "ten" is the darkest dark you can achieve on your paper. In addition, each number value has a light, medium and dark component to it so I might refer to an 8 light, 8 medium, or 8 dark in my instructions. Print this grayscale so that you will have it to refer to.