Electron-beam writer characterization is key to enable predictable product performance in a photomask shop. This is traditionally done by writing test patterns with one distinct tool on one blank. Within this article, we introduce a method that reduces uncertainty caused by variation of blanks and process parameters, by using multiple, subsequent electronbeam exposure steps with different same-of-a-kind tools. The method is demonstrated for the disentanglement of two of the most fundamental parameters in an e-beam tool, current density and blanker latency, which together determine the actual dose. Additional accuracy can be achieved by probing the same tool parameter with different methods, which is shown by comparing Critical Dimension Scanning Electron Microscopy of line-space patterns below the maximum shot size with Thin Film Optical Scatterometry of comparatively large pads. The multiple exposure method needs a proper correction of systematic effects caused by contact of exposed areas with air during mask transfer from one writer to another, which are presented and discussed.