High precision mapping of the vacuum flux surfaces of the H-1NF heliac is carried out using electron-beam multi-wire tomography for various magnetic configurations and field strengths. The extreme accuracy of this technique has been exploited to understand the nature of error fields and to determine the best-fit empirical values for the H-1NF coil parameters, by point-by-point matching experimental surface data with computer modelling results. This has helped in developing a highly accurate computer model for H-1NF magnetic configurations.