WISRD Research & Engineering Journal

2.6 Rulers To manually measure differences in the growth of the coral, we attached physical rulers to the rack. Unfortunately, it was difficult to easily distinguish the contrast between the white ruler, which looks blue under the tank lights, and light-colored coral fragments. The solution was to trim the ruler to minimize the white so all that was visible were the millimeter markings as shown in Figure 9. We used a 45W CO 2 laser to trim the length of the ruler as close to the measurement lines as possible. The narrower rulers also fit within the open spaces of the frag rack and could be epoxied in place against the inside face of a square within the rack.

Figure 9 . Rulers cut lengthwise to make markings more visible. Five rulers were affixed, and the fragments were clustered around them to fit within the width of a photograph taken by a Raspberry Pi at a distance of approximately 18 cm from the glass of the tank. (Figure 10.) The positioning of the camera is discussed in the next section.

Figure 10 . Five rulers spaced out across the Pi camera’s field of view.

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