The pressure gradient required to force water through a straight horizontal $1 / 4 \mathrm{in}$. ID tube at a rate of $2 \mathrm{gpm}$ is $1.2 \mathrm{psi} / \mathrm{ft}$. Consider this same tubing coiled in an expanding helix with a vertical axis. Water enters the bottom of the coil and flows upward at a rate of $2 \mathrm{gpm}$. A mercury manometer is connected between two pressure taps on the coil, one near the bottom where the coil radius is $6 \mathrm{in}$., and the other near the top where the coil radius is $12 \mathrm{in}$. The taps are $2 \mathrm{ft}$ apart in the vertical direction, and there is a total of $5 \mathrm{ft}$ of tubing between the two taps. Determine the manometer reading, in $\mathrm{cm}$.