Excerpt from Friction Factors for Helical Corrugated Pipe A scale, graduated in hundredths of afoot, was placed behind the glass tubes. The water level was read by eye to the nearest hundredth of a foot. To improve the precision of the manometer measurements the simple manometers were re placed with l-l/2-inch-diameter glass tubes and point gages which could be read to the nearest foot. These tubes were grouped on one frame, as shown in figure 3, so they could be coupled to a common header pipe for the simultaneous zeroing of the eight point gages with a common water level. This was a significant improvement over the zeroing of the individual manometers which were zeroed by using an engineer's level. Although the grouping of the manometers on one frame greatly reduced zeroing errors, it did require long hose lines from the static tubes to the manometers with attendant air bubble trouble. The use of clear plastic tubing for these lines reduced the bubble problem in that the lines could be inspected frequently. If bubbles were present, they could be easily bled out of the lines.

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