Axial ratio-fluctuation measurements made on markers (oncolites, oolites, quartz grains, and accretionary lapilli) on bedding-perpendicular sections of unstrained sedimentary rocks have been homogeneously strained mathematically by set amounts, using published transformation equations, to provide a simulation of natural tectonic deformation. The resultant data have been used as test input to the strain analysis computer programs of Dunnet and Siddans (1971) and Matthews et al. (1974), which were devised to assess tectonic strain in assemblages of strained elliptical markers, with the use of limited specific assumptions concerning the nature of the pre-tectonic fabrics of the markers. The tests have shown that even slight deviations in the initial fabrics from the assumptions involved in the use of the strain analysis methods may lead to significant errors in the strain determinations. Errors are particularly large when fabrics which were imbricate in the unstrained state are used with the mistaken assumption that they were bedding-symmetric. © 1979.