The mechanic also reported that on September 29, 2000, he removed the right side attitude indicator for overhaul37 and installed a placard on the instrument panel that stated, "CO-PILOTS HORIZON GYRO REMOVED FOR O/H 9/29/00." The mechanic stated that the pilot had called him on October 9th or 10th to check on the status of the right-side attitude indicator (referred to here as the "co-pilot's horizon gyro"). According to the mechanic, during this conversation, the pilot told him that since the removal of the part, the vacuum gage had been reading lower than "what he was accustomed to seeing." The mechanic stated that he explained to the pilot that "the removed instrument is a restriction on the vacuum system and since it had been removed, that was the most likely reason for the lower reading.