aquatube Gauge ¶ The aquatube Gauge can visualize percentages as a big or small aquatube image with an accordant water level. Representations of various percentages. The water layer is semi-transparent, while the front plate is opaque with a transparent cut-out in the center. The back plate is fully opaque. It uses the GD graphics library, a common image manipulation package that has wrappers for numerous programming languages (including PHP).