Described is a system and method for training a machine learning network. The hitch or hitch bar adapter holds one ball at a first height and a second ball at a second height different from the first. Left and right handles are preferably secured to upper ends of respective intermediate links to provide coordinated arm and leg exercise motion. Further, because the liquid can constantly exist on the image plane side of the projection optical system, generation of water marks on optical members of the projection optical system on the image plane side is prevented. The preferred orthophosphates are one or more of monosodium dihydrogen orthophosphate, disodium hydrogen orthophosphate, trisodium orthophosphate, monopotassium dihydrogen orthophosphate, dipotassium hydrogen orthophosphate and tri potassium orthophosphate. The magnetostrictive element is characterized by having a distinct magnetostrictive effect.