Applying laser-speckle techniques in material sciences as well as in methods to characterize surface conditions of specimen has become the method of choice, especially if a non-contacting principle is sought. This is almost always the case for specimen that are small in at least one dimension as for example in the material testing of foils, fibres, or micromaterials and certainly also if elevated test-temperatures are preventing standard gauges. This letter discusses in some detail sources of error that are quite often overlooked or not even considered as signiˉcant at all, but still carry the potential to introduce uncertainties well above the system design specifications.