“…The analyses of strain in the primary shear zone (PSZ) have mainly been carried out producing a grid of lines or chess board grids. Mechanical abrasion methods for producing grid lines were described by Baraya et al (1963) as satisfactory for most work when milling cutters are employed, achieving up to 4 lines/mm. Childs (Childs, 1971) employed a micro-hardness diamond for scratching the work-piece surface achieving a density of 40 lines/mm.…”