“…Variations include holographic interferometry [11][12][13][14][15][16][17][18], moiré interferometry [19,20], shearography [21][22][23][24] and electronic (or digital) speckle pattern interferometry, ESPI [25]. The last of these methods has been applied in connection with stress relaxation by hole drilling [26][27][28][29][30][31], local heating [32][33][34][35], chemical etching of a strip [36,37] and incremental groove machining [38,39].…”