A 3D space can be reconstructed from the images produced by a pair of digital vision sen-sors. However, due to the digital sensor the reconstructed space is discretized and its quanti-sation levels are defined by the iso-disparity surfaces. Thus, the accuracy of the space depth reconstruction is related to the iso-disparity map. A validation of the reconstruction techniques requires a measurement with a high accu-racy reference. This paper introduces an easily implemented method based on a differential depth measurement. The modelling and analysis of the quantization uncertainty of the depth and differential depth measurements is presented in the paper. The model is verified through simulations, and further verified by a physical experiment.