The 12:00 on your digital device is not the same as the Solar Noon (as per a a sun dial), to calculate the digital time for your Solar Noon check out this web-site (see below, thank "gawd" for clever people who can do mathematics that I cannot):
https://gml.noaa.gov/grad/solcalc/
Courtesy of the ESRL Global Monitoring Laboratory, a big thank you to you!
