The aim of this study was to determine the extent of upper arm, neck and trunk posture variation that can be obtained by combining seated and standing computer work, compared to performing only seated computer work. Posture data were recorded for two hours during each of three days of ordinary work from 24 office workers that had been using a sit-stand station for two months. Periods with sitting and standing computer work were identified using on-site observations, and posture means and minute-to-minute variance were determined for both. Expected minute-to-minute posture variability in different temporal combinations of sitting and standing computer work were determined by simulation, and expressed in terms of a Job Variance Ratio, i.e. the relative increase in variability compared to sitting-only work. For all three postures, mean values differed between sitting and standing computer work, and both showed a notable minute-to-minute variability. For most workers, posture variability was larger when combining sitting and standing than when sitting only, and simulations suggested to introduce more standing than what the worker currently practiced. The results indicate that introducing a sit-stand table could, for most office workers, have a positive effect on upper arm, neck and trunk posture variability.