HOPG SPI Supplies® Brand Grade SPI-1 20x20x0.7 mm Thick, Pack of 1 Piece

Very similar to Grade ZYA described below and is comparable to the very best "calibration grade" HOPG and exhibiting a 0.4° +/- 0.1° (demonstrating outstanding crystalline perfection) but lower in price than other HOPGs of comparable quality. This is the most highly ordered, lateral grain size is typically up to about 3 mm but can be as large as 10 mm, and is used primarily for instrument calibration purposes or for research experiments where for some reason, the very ultimate in HOPG order is needed. This is the highest quality material and also the most expensive. Suitable for the most critical calibration requirements and research applications.