Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In five consecutive sections, five measurements of GCL width were performed at 25 μm intervals (Haas et al., 2002; Houser, 1990) using AxioVision software (Carl Zeiss AG, Oberkochen, Germany).
Category: