Recently, an advertiser wrote into the AdWords support team, alarmed that his average CPC had increased suddenly from $0.65 to $1.40. He had no idea what caused this spike, nor could he recall making any recent changes that would prompt such a dramatic increase. Fortunately, the My Change History tool, which is available within all advertiser accounts, is invaluable in uncovering factors that may lead to unexpected account behavior. I helped the advertiser filter his account’s CPC changes and we found that a few days earlier, a user with his same AdWords account login had, in fact, increased a campaign’s maximum CPCs to $1.60. This change would explain the dramatic increase in average CPC.Even after seeing his account's logged changes, the advertiser still could not recall making the CPC increases and thought it must have been an error. Just to be sure, he checked with his manager who rarely makes changes to the account but does login on occasion. It turned out the CPC increases were in fact, made by his manager and were not an error. To avoid any future confusion over account changes, I suggested that he and his manager make use of multiple logins.If several individuals make changes to the same AdWords account, but are sharing one user login and password, troubleshooting account changes using the My Change History tool can be difficult or impossible. With multiple logins, each person can create their own AdWords login and password and any changes they make will be recorded in My Change History under their respective login.Once we got everything straightened out, the advertiser was happy to know that he could always turn to the My Change History tool to troubleshoot any account problems easily, especially now that he and his manager were using their own separate logins.