solar noon dial. measures not the hourly cycle of the sun but its cycle across the seasons. the reading is taken at the sun’s zenith at noon, along a single meridian line, oriented north/south. it is intended for the accurate determination of the equinoxes and solstices. traditionally It has a nodus rather than a full gnomon, and may be in the form of a small ball on the end of a shaft or, more usually, a small circular aperture projecting a image of the sun onto the floor of the building. very long meridian lines were built into cathedrals. the basilica di danta maria degli angeli e dei martiri in rome has such a line. see last two photos zennor hill sunstone seems to fit this description. this is an upturned, stone solutions basin positioned some 5* short of the vertical, with the basin’s surface oriented north to south. a small hole and notch in the basin’s rim projects the sun’s rays across its surface each day at the solar noon, so that it’s changing angle can reflect the changing seasons. a careful noting of its position would reveal the timing of the yearly solstices and equinoxes in much the same way as a solar noon dial. photo dated june 21 11.27 2014