I am a Civil Engineer with limited survey knowledge and have been reviewing geodetic concepts and the subject of vertical datum. In the civil engineering profession, many times a day I see reference to MSL but know the surveyor has indicated NAVD88 as the vertical datum. It seems that anything related to tide stations such as NAVD88 or NGVD1929 would in some way be considered MSL. However, it remains a source of confusion, as a novice surveyor, I am unfamiliar with the surveyor definition of MSL. Can someone elaborate on the difference(s) between "MSL" and NAVD88, if any ?