GAUGE MARKERS, 1 WHITE DIAMOND ON BLACK BACKGROUND, 400 PIECES, TRVIEWX. 1 white diamond on a black background gauge markers for TRViewX non-contact video extensometers and width sensors. These gauge markers are suitable for flat dark plastic and flat dark metal specimens with 20 mm or below gauge length or for width measurements, have a temperature range of -20 to 150?C, and include 400 pieces..