In one of the largest and most extensive measurement campaigns to date, the measuring systems for lightning impulses (LI) of the National Metrology Institutes (NMIs) of Germany (PTB), Sweden (RISE) and Finland (VTT MIKES) have been compared. In the high-voltage laboratory of PTB, lightning impulse comparisons were carried out at voltages up to 1500 kV. The test voltage, front time, time to half-value and the relative overshoot magnitude of seven systems have been compared. The results confirm the capabilities and uncertainties of the participating metrology institutes and even enable an improvement of those. Finally, the question, whether an uncertainty of less than 0.5 % for peak values and 1 % for time parameters for NMI reference measuring systems for a lightning impulse up to at least 800 kV is achievable, will be addressed.