In my last 4.0 match, we were playing on clay. My partner was near the baseline in the deuce court; I was at net in the ad court. Opponents hit a ball wide to her which landed near the deuce sideline. She called the ball out. I didn't get a good look at it, but it could well have been in. I wasn't certain enough to overrule my partner, who was right there in position to make the call. Opponents expressed disgust at the call. After my partner had started walking back to the baseline to serve again, one of them asked her to check the mark. She said they had delayed in making this request and could not ask her to check the mark. She went over and said she didn't see a mark. Me, I stood there saying nothing and doing nothing because I didn't know what to say or to do. My partner then asked me if they had waited too long. I shrugged. OK. What is the proper protocol for checking marks on clay and for making requests? I know the opponent is not permitted to come across to the other side to inspect a mark (Thanks, Martina Hingis!). What happens if the players disagree about which is the correct mark? How promptly must the request to check be made? What if the request to check the mark is refused? What if I don't know what the mark means? If I call a point-ending ball good, can I go over, inspect the mark, declare it out, and then take the point? Would my opponent be justified in strangling me to death on the spot if I attempted such a thing? Here's what the Code says: I have played on clay a lot, and often the courts are so banged up that it is difficult to find or interpret ball marks. No one has ever asked me to check a ball mark (other than my own partner!). Nor have I ever asked an opponent to do it. Now I am wondering whether I should start making such a request, as there have been many, many occasions where I heard the ball smack the tape and the opponent called it out anyway.