Recently I read that one of the pre-conditions (among many others) of a successful lift off of the LM ascend stage, from the moon surface, was that the LM ascend stage "axis" should be "vertical" (normal to lunar surface) within 12 degrees. Given the uncertainty of lunar surface "flatness" at the time of landing, how did NASA ensure that the axis will be vertical within 12 degree? Was any specific mechanism provided to ensure this? Or was it a calculated risk and optimism?