Mine was a mess so I went ahead and washed it. It was so bad I figured I had nothing to lose. I stood it on its side in the sink and wet it down with a water/liquid detergent mixture. Let it sit a while then scrubbed with a brush. I think I even used a light bleach mixture on one section - it was that dirty. Then I pressed out as much water as I could, rinsed under the faucet, pressed out the water. Kept rinsing until I got all the detergent out. Then hung outside in the sunshine to dry. It turned out great. I never use my pad for measuring so I don't know if this messed up the marking.