Shreck - You need to make sure you have calibrated your equipment. Once you have done that, open the picture of/with the gray card on it (make sure you are using a good color profile for the document). You can send a print directly to the printer now and see if it matches your screen. If you want to do any color adjustments, you can use the grey card as a reference. Use the color info dropper (the eye dropper that lets you put multiple reticles on the screen). Click on the gray card and adjust your levels/curves/color until you have 18% gray showing in the info palette. Then send a print and compare with your document and with your original gray card.