Disclosed herein is a deadweight loading apparatus, system, and method for calibrating a testing device. The deadweight loading apparatus comprises a cart, comprising a horizontal support surface, a cart handle, a plurality of weights stackable on the horizontal support surface, and a basket supportable on the horizontal support surface. The basket comprising a first side plate and a second side plate. The apparatus also comprises a selector bar comprising two extension arms that are selectively, adjustably, engageable with the first side plate and the second side plate at each one of multiple vertical locations along the first side plate and the second side plate. When the selector bar is selectively, adjustably, engaged with the first side plate and the second side plate, each one of the two extension arms is fitted within a corresponding one of the two grooves on a corresponding weight.