Sun Dial Time Corrections

Corrections need to be made in order to obtain Mean time from a sundial. 

These are:

  • Correction for the Equation of Time
  • Correction for Longitude
  • Correction for Summer Time

These are considered in turn below:

Want a little card to carry with you to help you check a sundial's displayed time at ANY Longitude or Latitude in the British Isles?  Hurry if you want one of the few remaining printed versions...

Click the picture for more details!

Click to download the Estimator

The equation of time describes the discrepancy between two kinds of solar time. These are Apparent Solar Time, which directly tracks the motion of the sun, and Mean Solar Time, which tracks a fictitious "mean" sun with noons 24 hours apart. Apparent (or true) solar time is that indicated by a sundial. Mean solar time, for the same place, would be the time indicated by a steady clock set so that over the year its differences from apparent solar time average to zero. Why not get The Recorder's Reference? It provides anyone interested in dialling with a way to estimate by how much a non-direct-south vertical dial declines and also finds the design latitude for any horizontal dial. 

Click the picture for more details!

I - Equation of Time Correction - 2018 & 2019 (Still want EoT for 2017? or 2016?)
This page P.Powers 2013, 2014, 2015, 2016, 2017, 2018 All Rights Reserved

The figures in the tables below show more accurate figures in mins and secs by which a sundial should be corrected during the whole of 2018 and 2019.  A link is also included to a printable page of the 2016 and 2017 EoT figures. The figures in the tables represent the Equation of Time at 12Hrs (Noon) GMT on the date stated and are here calculated using the method after Smart (1956) which is accurate at worst to about 4 secs - frequently to one second..  Interpolation will of course, be necessary if an EoT is needed for times other than Noon. Note that in non-leap-years there is still an entry in the tables for Feb 29th but its value is then the same as that for Mar 1st. NB Don't forget the two other corrections for longitude and daylight saving time...

Negative values in the table indicate Dial Slow.

Equation of Time Correction - 2018 (also 2019 and 2017 )
2018 One Page Printable version of 2018 EoT 2019 One Page Printable version of 2019 EoT
Jan-01 -3m 34s   May-01 2m 54s   Sep-01 -0m 2s
Jan-02 -4m 2s   May-02 3m 1s   Sep-02 0m 18s
Jan-03 -4m 29s   May-03 3m 7s   Sep-03 0m 37s
Jan-04 -4m 57s   May-04 3m 13s   Sep-04 0m 57s
Jan-05 -5m 24s   May-05 3m 18s   Sep-05 1m 17s
Jan-06 -5m 50s   May-06 3m 23s   Sep-06 1m 37s
Jan-07 -6m 16s   May-07 3m 27s   Sep-07 1m 57s
Jan-08 -6m 41s   May-08 3m 30s   Sep-08 2m 18s
Jan-09 -7m 7s   May-09 3m 33s   Sep-09 2m 38s
Jan-10 -7m 31s   May-10 3m 35s   Sep-10 2m 59s
Jan-11 -7m 55s   May-11 3m 37s   Sep-11 3m 20s
Jan-12 -8m 18s   May-12 3m 38s   Sep-12 3m 41s
Jan-13 -8m 41s   May-13 3m 39s   Sep-13 4m 3s
Jan-14 -9m 3s   May-14 3m 39s   Sep-14 4m 24s
Jan-15 -9m 24s   May-15 3m 39s   Sep-15 4m 45s
Jan-16 -9m 45s   May-16 3m 38s   Sep-16 5m 7s
Jan-17 -10m 5s   May-17 3m 36s   Sep-17 5m 28s
Jan-18 -10m 25s   May-18 3m 34s   Sep-18 5m 50s
Jan-19 -10m 43s   May-19 3m 31s   Sep-19 6m 11s
Jan-20 -11m 1s   May-20 3m 28s   Sep-20 6m 32s
Jan-21 -11m 18s   May-21 3m 24s   Sep-21 6m 54s
Jan-22 -11m 35s   May-22 3m 20s   Sep-22 7m 15s
Jan-23 -11m 50s   May-23 3m 15s   Sep-23 7m 36s
Jan-24 -12m 5s   May-24 3m 9s   Sep-24 7m 57s
Jan-25 -12m 19s   May-25 3m 3s   Sep-25 8m 18s
Jan-26 -12m 33s   May-26 2m 57s   Sep-26 8m 39s
Jan-27 -12m 45s   May-27 2m 50s   Sep-27 8m 59s
Jan-28 -12m 57s   May-28 2m 43s   Sep-28 9m 19s
Jan-29 -13m 8s   May-29 2m 35s   Sep-29 9m 39s
Jan-30 -13m 18s   May-30 2m 27s   Sep-30 9m 59s
Jan-31 -13m 27s   May-31 2m 18s   Oct-01 10m 19s
Feb-01 -13m 35s   Jun-01 2m 9s   Oct-02 10m 38s
Feb-02 -13m 43s   Jun-02 1m 60s   Oct-03 10m 57s
Feb-03 -13m 50s   Jun-03 1m 50s   Oct-04 11m 16s
Feb-04 -13m 56s   Jun-04 1m 40s   Oct-05 11m 34s
Feb-05 -14m 1s   Jun-05 1m 29s   Oct-06 11m 52s
Feb-06 -14m 5s   Jun-06 1m 19s   Oct-07 12m 10s
Feb-07 -14m 9s   Jun-07 1m 8s   Oct-08 12m 27s
Feb-08 -14m 11s   Jun-08 0m 56s   Oct-09 12m 44s
Feb-09 -14m 13s   Jun-09 0m 44s   Oct-10 12m 60s
Feb-10 -14m 14s   Jun-10 0m 33s   Oct-11 13m 16s
Feb-11 -14m 14s   Jun-11 0m 20s   Oct-12 13m 31s
Feb-12 -14m 14s   Jun-12 0m 8s   Oct-13 13m 46s
Feb-13 -14m 13s   Jun-13 -0m 4s   Oct-14 14m 0s
Feb-14 -14m 11s   Jun-14 -0m 17s   Oct-15 14m 14s
Feb-15 -14m 8s   Jun-15 -0m 30s   Oct-16 14m 27s
Feb-16 -14m 5s   Jun-16 -0m 43s   Oct-17 14m 40s
Feb-17 -14m 0s   Jun-17 -0m 56s   Oct-18 14m 52s
Feb-18 -13m 56s   Jun-18 -1m 9s   Oct-19 15m 3s
Feb-19 -13m 50s   Jun-19 -1m 22s   Oct-20 15m 14s
Feb-20 -13m 44s   Jun-20 -1m 35s   Oct-21 15m 24s
Feb-21 -13m 37s   Jun-21 -1m 48s   Oct-22 15m 34s
Feb-22 -13m 29s   Jun-22 -2m 1s   Oct-23 15m 42s
Feb-23 -13m 21s   Jun-23 -2m 14s   Oct-24 15m 50s
Feb-24 -13m 12s   Jun-24 -2m 27s   Oct-25 15m 58s
Feb-25 -13m 3s   Jun-25 -2m 39s   Oct-26 16m 4s
Feb-26 -12m 53s   Jun-26 -2m 52s   Oct-27 16m 10s
Feb-27 -12m 43s   Jun-27 -3m 5s   Oct-28 16m 15s
Feb-28 -12m 32s   Jun-28 -3m 17s   Oct-29 16m 20s
Feb-29 -12m 20s   Jun-29 -3m 29s   Oct-30 16m 23s
Mar-01 -12m 20s   Jun-30 -3m 41s   Oct-31 16m 26s
Mar-02 -12m 8s   Jul-01 -3m 53s   Nov-01 16m 28s
Mar-03 -11m 55s   Jul-02 -4m 4s   Nov-02 16m 29s
Mar-04 -11m 42s   Jul-03 -4m 15s   Nov-03 16m 29s
Mar-05 -11m 29s   Jul-04 -4m 26s   Nov-04 16m 29s
Mar-06 -11m 15s   Jul-05 -4m 36s   Nov-05 16m 27s
Mar-07 -11m 1s   Jul-06 -4m 47s   Nov-06 16m 25s
Mar-08 -10m 46s   Jul-07 -4m 56s   Nov-07 16m 22s
Mar-09 -10m 31s   Jul-08 -5m 6s   Nov-08 16m 18s
Mar-10 -10m 16s   Jul-09 -5m 15s   Nov-09 16m 13s
Mar-11 -9m 60s   Jul-10 -5m 23s   Nov-10 16m 8s
Mar-12 -9m 44s   Jul-11 -5m 32s   Nov-11 16m 1s
Mar-13 -9m 28s   Jul-12 -5m 39s   Nov-12 15m 54s
Mar-14 -9m 11s   Jul-13 -5m 47s   Nov-13 15m 46s
Mar-15 -8m 54s   Jul-14 -5m 53s   Nov-14 15m 37s
Mar-16 -8m 37s   Jul-15 -5m 60s   Nov-15 15m 27s
Mar-17 -8m 20s   Jul-16 -6m 5s   Nov-16 15m 16s
Mar-18 -8m 3s   Jul-17 -6m 11s   Nov-17 15m 4s
Mar-19 -7m 45s   Jul-18 -6m 15s   Nov-18 14m 52s
Mar-20 -7m 27s   Jul-19 -6m 20s   Nov-19 14m 39s
Mar-21 -7m 9s   Jul-20 -6m 23s   Nov-20 14m 25s
Mar-22 -6m 51s   Jul-21 -6m 26s   Nov-21 14m 10s
Mar-23 -6m 33s   Jul-22 -6m 29s   Nov-22 13m 54s
Mar-24 -6m 15s   Jul-23 -6m 31s   Nov-23 13m 37s
Mar-25 -5m 57s   Jul-24 -6m 32s   Nov-24 13m 20s
Mar-26 -5m 39s   Jul-25 -6m 33s   Nov-25 13m 2s
Mar-27 -5m 21s   Jul-26 -6m 33s   Nov-26 12m 43s
Mar-28 -5m 3s   Jul-27 -6m 32s   Nov-27 12m 24s
Mar-29 -4m 45s   Jul-28 -6m 31s   Nov-28 12m 4s
Mar-30 -4m 27s   Jul-29 -6m 30s   Nov-29 11m 43s
Mar-31 -4m 9s   Jul-30 -6m 27s   Nov-30 11m 21s
Apr-01 -3m 51s   Jul-31 -6m 25s   Dec-01 10m 59s
Apr-02 -3m 33s   Aug-01 -6m 21s   Dec-02 10m 36s
Apr-03 -3m 16s   Aug-02 -6m 17s   Dec-03 10m 12s
Apr-04 -2m 58s   Aug-03 -6m 12s   Dec-04 9m 48s
Apr-05 -2m 41s   Aug-04 -6m 7s   Dec-05 9m 24s
Apr-06 -2m 24s   Aug-05 -6m 1s   Dec-06 8m 58s
Apr-07 -2m 7s   Aug-06 -5m 55s   Dec-07 8m 33s
Apr-08 -1m 51s   Aug-07 -5m 47s   Dec-08 8m 7s
Apr-09 -1m 34s   Aug-08 -5m 40s   Dec-09 7m 40s
Apr-10 -1m 18s   Aug-09 -5m 31s   Dec-10 7m 13s
Apr-11 -1m 2s   Aug-10 -5m 23s   Dec-11 6m 45s
Apr-12 -0m 47s   Aug-11 -5m 13s   Dec-12 6m 18s
Apr-13 -0m 32s   Aug-12 -5m 3s   Dec-13 5m 49s
Apr-14 -0m 17s   Aug-13 -4m 53s   Dec-14 5m 21s
Apr-15 -0m 2s   Aug-14 -4m 42s   Dec-15 4m 52s
Apr-16 0m 12s   Aug-15 -4m 30s   Dec-16 4m 23s
Apr-17 0m 26s   Aug-16 -4m 18s   Dec-17 3m 54s
Apr-18 0m 40s   Aug-17 -4m 5s   Dec-18 3m 25s
Apr-19 0m 53s   Aug-18 -3m 52s   Dec-19 2m 55s
Apr-20 1m 5s   Aug-19 -3m 38s   Dec-20 2m 26s
Apr-21 1m 17s   Aug-20 -3m 24s   Dec-21 1m 56s
Apr-22 1m 29s   Aug-21 -3m 10s   Dec-22 1m 26s
Apr-23 1m 41s   Aug-22 -2m 54s   Dec-23 0m 56s
Apr-24 1m 52s   Aug-23 -2m 39s   Dec-24 0m 27s
Apr-25 2m 2s   Aug-24 -2m 23s   Dec-25 -0m 3s
Apr-26 2m 12s   Aug-25 -2m 7s   Dec-26 -0m 33s
Apr-27 2m 21s   Aug-26 -1m 50s   Dec-27 -1m 2s
Apr-28 2m 30s   Aug-27 -1m 33s   Dec-28 -1m 32s
Apr-29 2m 39s   Aug-28 -1m 15s   Dec-29 -2m 1s
Apr-30 2m 47s   Aug-29 -0m 57s   Dec-30 -2m 30s
      Aug-30 -0m 39s   Dec-31 -2m 58s
      Aug-31 -0m 20s      


Jan 01 -3m 27s   May 01 2m 52s   Sep 01 -0m 6s
Jan 02 -3m 55s   May 02 2m 59s   Sep 02 0m 13s
Jan 03 -4m 23s   May 03 3m 5s   Sep 03 0m 32s
Jan 04 -4m 50s   May 04 3m 11s   Sep 04 0m 52s
Jan 05 -5m 17s   May 05 3m 17s   Sep 05 1m 12s
Jan 06 -5m 43s   May 06 3m 21s   Sep 06 1m 32s
Jan 07 -6m 10s   May 07 3m 26s   Sep 07 1m 52s
Jan 08 -6m 35s   May 08 3m 29s   Sep 08 2m 13s
Jan 09 -7m 0s   May 09 3m 32s   Sep 09 2m 33s
Jan 10 -7m 25s   May 10 3m 35s   Sep 10 2m 54s
Jan 11 -7m 49s   May 11 3m 37s   Sep 11 3m 15s
Jan 12 -8m 12s   May 12 3m 38s   Sep 12 3m 36s
Jan 13 -8m 35s   May 13 3m 39s   Sep 13 3m 57s
Jan 14 -8m 57s   May 14 3m 39s   Sep 14 4m 19s
Jan 15 -9m 19s   May 15 3m 39s   Sep 15 4m 40s
Jan 16 -9m 40s   May 16 3m 38s   Sep 16 5m 2s
Jan 17 -10m 0s   May 17 3m 36s   Sep 17 5m 23s
Jan 18 -10m 20s   May 18 3m 34s   Sep 18 5m 44s
Jan 19 -10m 39s   May 19 3m 32s   Sep 19 6m 6s
Jan 20 -10m 57s   May 20 3m 28s   Sep 20 6m 27s
Jan 21 -11m 14s   May 21 3m 25s   Sep 21 6m 48s
Jan 22 -11m 31s   May 22 3m 21s   Sep 22 7m 10s
Jan 23 -11m 47s   May 23 3m 16s   Sep 23 7m 31s
Jan 24 -12m 2s   May 24 3m 11s   Sep 24 7m 52s
Jan 25 -12m 16s   May 25 3m 5s   Sep 25 8m 13s
Jan 26 -12m 29s   May 26 2m 59s   Sep 26 8m 34s
Jan 27 -12m 42s   May 27 2m 52s   Sep 27 8m 54s
Jan 28 -12m 54s   May 28 2m 45s   Sep 28 9m 14s
Jan 29 -13m 5s   May 29 2m 37s   Sep 29 9m 35s
Jan 30 -13m 15s   May 30 2m 29s   Sep 30 9m 55s
Jan 31 -13m 25s   May 31 2m 20s   Oct 01 10m 14s
Feb 01 -13m 33s   Jun 01 2m 11s   Oct 02 10m 34s
Feb 02 -13m 41s   Jun 02 2m 2s   Oct 03 10m 53s
Feb 03 -13m 48s   Jun 03 1m 52s   Oct 04 11m 11s
Feb 04 -13m 54s   Jun 04 1m 42s   Oct 05 11m 30s
Feb 05 -13m 59s   Jun 05 1m 32s   Oct 06 11m 48s
Feb 06 -14m 4s   Jun 06 1m 21s   Oct 07 12m 6s
Feb 07 -14m 8s   Jun 07 1m 10s   Oct 08 12m 23s
Feb 08 -14m 10s   Jun 08 0m 59s   Oct 09 12m 40s
Feb 09 -14m 13s   Jun 09 0m 47s   Oct 10 12m 56s
Feb 10 -14m 14s   Jun 10 0m 35s   Oct 11 13m 12s
Feb 11 -14m 14s   Jun 11 0m 23s   Oct 12 13m 27s
Feb 12 -14m 14s   Jun 12 0m 11s   Oct 13 13m 42s
Feb 13 -14m 13s   Jun 13 -0m 1s   Oct 14 13m 57s
Feb 14 -14m 11s   Jun 14 -0m 14s   Oct 15 14m 11s
Feb 15 -14m 9s   Jun 15 -0m 27s   Oct 16 14m 24s
Feb 16 -14m 5s   Jun 16 -0m 40s   Oct 17 14m 37s
Feb 17 -14m 1s   Jun 17 -0m 53s   Oct 18 14m 49s
Feb 18 -13m 57s   Jun 18 -1m 6s   Oct 19 15m 1s
Feb 19 -13m 51s   Jun 19 -1m 19s   Oct 20 15m 11s
Feb 20 -13m 45s   Jun 20 -1m 32s   Oct 21 15m 22s
Feb 21 -13m 39s   Jun 21 -1m 45s   Oct 22 15m 31s
Feb 22 -13m 31s   Jun 22 -1m 58s   Oct 23 15m 40s
Feb 23 -13m 23s   Jun 23 -2m 11s   Oct 24 15m 48s
Feb 24 -13m 15s   Jun 24 -2m 24s   Oct 25 15m 56s
Feb 25 -13m 5s   Jun 25 -2m 36s   Oct 26 16m 3s
Feb 26 -12m 55s   Jun 26 -2m 49s   Oct 27 16m 9s
Feb 27 -12m 45s   Jun 27 -3m 2s   Oct 28 16m 14s
Feb 28 -12m 34s   Jun 28 -3m 14s   Oct 29 16m 19s
Feb 29 -12m 23s   Jun 29 -3m 26s   Oct 30 16m 22s
Mar 01 -12m 23s   Jun 30 -3m 38s   Oct 31 16m 25s
Mar 02 -12m 11s   Jul 01 -3m 50s   Nov 01 16m 27s
Mar 03 -11m 58s   Jul 02 -4m 1s   Nov 02 16m 29s
Mar 04 -11m 45s   Jul 03 -4m 13s   Nov 03 16m 29s
Mar 05 -11m 32s   Jul 04 -4m 24s   Nov 04 16m 29s
Mar 06 -11m 18s   Jul 05 -4m 34s   Nov 05 16m 28s
Mar 07 -11m 4s   Jul 06 -4m 44s   Nov 06 16m 26s
Mar 08 -10m 50s   Jul 07 -4m 54s   Nov 07 16m 23s
Mar 09 -10m 35s   Jul 08 -5m 4s   Nov 08 16m 19s
Mar 10 -10m 19s   Jul 09 -5m 13s   Nov 09 16m 15s
Mar 11 -10m 4s   Jul 10 -5m 22s   Nov 10 16m 9s
Mar 12 -9m 48s   Jul 11 -5m 30s   Nov 11 16m 3s
Mar 13 -9m 31s   Jul 12 -5m 38s   Nov 12 15m 56s
Mar 14 -9m 15s   Jul 13 -5m 45s   Nov 13 15m 48s
Mar 15 -8m 58s   Jul 14 -5m 52s   Nov 14 15m 39s
Mar 16 -8m 41s   Jul 15 -5m 58s   Nov 15 15m 29s
Mar 17 -8m 24s   Jul 16 -6m 4s   Nov 16 15m 19s
Mar 18 -8m 7s   Jul 17 -6m 10s   Nov 17 15m 7s
Mar 19 -7m 49s   Jul 18 -6m 14s   Nov 18 14m 55s
Mar 20 -7m 31s   Jul 19 -6m 19s   Nov 19 14m 42s
Mar 21 -7m 14s   Jul 20 -6m 22s   Nov 20 14m 28s
Mar 22 -6m 56s   Jul 21 -6m 26s   Nov 21 14m 13s
Mar 23 -6m 38s   Jul 22 -6m 28s   Nov 22 13m 58s
Mar 24 -6m 20s   Jul 23 -6m 30s   Nov 23 13m 42s
Mar 25 -6m 2s   Jul 24 -6m 32s   Nov 24 13m 24s
Mar 26 -5m 43s   Jul 25 -6m 33s   Nov 25 13m 7s
Mar 27 -5m 25s   Jul 26 -6m 33s   Nov 26 12m 48s
Mar 28 -5m 7s   Jul 27 -6m 33s   Nov 27 12m 29s
Mar 29 -4m 49s   Jul 28 -6m 32s   Nov 28 12m 9s
Mar 30 -4m 31s   Jul 29 -6m 30s   Nov 29 11m 48s
Mar 31 -4m 13s   Jul 30 -6m 28s   Nov 30 11m 26s
Apr 01 -3m 55s   Jul 31 -6m 25s   Dec 01 11m 4s
Apr 02 -3m 38s   Aug 01 -6m 22s   Dec 02 10m 42s
Apr 03 -3m 20s   Aug 02 -6m 18s   Dec 03 10m 18s
Apr 04 -3m 3s   Aug 03 -6m 14s   Dec 04 9m 54s
Apr 05 -2m 45s   Aug 04 -6m 8s   Dec 05 9m 30s
Apr 06 -2m 28s   Aug 05 -6m 3s   Dec 06 9m 5s
Apr 07 -2m 11s   Aug 06 -5m 56s   Dec 07 8m 39s
Apr 08 -1m 55s   Aug 07 -5m 49s   Dec 08 8m 13s
Apr 09 -1m 38s   Aug 08 -5m 42s   Dec 09 7m 47s
Apr 10 -1m 22s   Aug 09 -5m 34s   Dec 10 7m 20s
Apr 11 -1m 6s   Aug 10 -5m 25s   Dec 11 6m 52s
Apr 12 -0m 50s   Aug 11 -5m 16s   Dec 12 6m 24s
Apr 13 -0m 35s   Aug 12 -5m 6s   Dec 13 5m 56s
Apr 14 -0m 20s   Aug 13 -4m 55s   Dec 14 5m 28s
Apr 15 -0m 6s   Aug 14 -4m 44s   Dec 15 4m 59s
Apr 16 0m 9s   Aug 15 -4m 33s   Dec 16 4m 30s
Apr 17 0m 23s   Aug 16 -4m 21s   Dec 17 4m 1s
Apr 18 0m 36s   Aug 17 -4m 8s   Dec 18 3m 32s
Apr 19 0m 49s   Aug 18 -3m 55s   Dec 19 3m 2s
Apr 20 1m 2s   Aug 19 -3m 42s   Dec 20 2m 33s
Apr 21 1m 15s   Aug 20 -3m 28s   Dec 21 2m 3s
Apr 22 1m 26s   Aug 21 -3m 13s   Dec 22 1m 33s
Apr 23 1m 38s   Aug 22 -2m 58s   Dec 23 1m 4s
Apr 24 1m 49s   Aug 23 -2m 43s   Dec 24 0m 34s
Apr 25 1m 59s   Aug 24 -2m 27s   Dec 25 0m 4s
Apr 26 2m 9s   Aug 25 -2m 11s   Dec 26 -0m 25s
Apr 27 2m 19s   Aug 26 -1m 54s   Dec 27 -0m 55s
Apr 28 2m 28s   Aug 27 -1m 37s   Dec 28 -1m 24s
Apr 29 2m 37s   Aug 28 -1m 20s   Dec 29 -1m 54s
Apr 30 2m 45s   Aug 29 -1m 2s   Dec 30 -2m 23s
      Aug 30 -0m 44s   Dec 31 -2m 51s
      Aug 31 -0m 25s      


Negative values in the table indicate Dial Slow.  

Accuracy - Just how accurate are these estimates of EoT?
The above EoT figures are calculated using Meeus's 'simpler' formula (after Smart) and are generally accurate to within 4 seconds and to less than 1 second for most of the year.
To illustrate this, the graph below shows the differences in seconds between Smart's EoT figures for 2012 and those of the Great Circle data when a detailed comparison was made.  
NB A further Excel comparison made over the year 2014 (that is two years later in the centre of that leap year cycle) may be found Here

II - Correction for Longitude

When a dial is not on the local Time Meridian, for example for a dial in the UK that is not on the actual Greenwich Meridian, then the sun is overhead at the dial at a time earlier or later than at Greenwich.  The correction to be made is 4 minutes of time for every degree of longitude difference from Greenwich.  This figure should be subtracted from the dial reading for dials East of Greenwich (such dials are Fast) and added for dials West of Greenwich. (such dials are Slow).

III - Correction for Summer Time

Lastly during the period when Summer Time (Daylight Saving Time) is in force one hour should be added to the corrected sundial reading to obtain clock time.

Finally, how about a simple in-the-pocket card that allows you to check a dial at any Latitude or Longitude in the British Isles, by converting its Solar time to Clock time?

Click on the image below to find out how!

Click to download the Estimator


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