Great app, i have tidetool for the palm which has a few other features :

option for different units, m, ft, inches
rise and set for sun - your gray scale ?
moon phases - 1st, full, last, new
currents, not for all locations

www.toolworks.com/bilofsky/tidetool

I also have RiseSet which gives major astronomical events such as elipses of sun/moon as well as rise/set for sun/moon. Gives the different civil, nautical & astronomical values for rise/set of sun. Gives current altide & azimuth in degrees of sun & moon.

www.40-below.com/palm