Sundials rarely agree with clocks.
Sundials tell what is called local apparent time.
The clocks in Panama City, Florida, for example, and those over 1100 miles to the west, in Lobo, Texas, show the same time but the sundials in the two cities differ by over an hour and twenty minutes. In order to convert your sundial time to standard time you must determine how much your longitude differs from that of your standard meridian, a north-south line somewhere in the middle of your time zone. Of course, if your standard meridian is to your west you will have to subtract, rather than add, the 4 minutes per degree. Another correction is also necessary. Because of the tilt of the earth's axis and the eccentricity of its orbit the rate at which the sun appears to travel through the sky varies throughout the year.