Until the 19th century, most European countries, even individual towns, used to indicate the local time on the basis of a well-defined astronomical measurement with a sundial.
Sundials were usually positioned so that they indicated 12 o'clock, when the Sun was seen directly South, that is at the moment of Local Noon. The local time of a town was therefore regulated in such a way that it was 12 o'clock at Local Noon.
Of course, in a modern society it is not very practical - indeed, it is quite impossible, to have different time indications across a country. Also, there should not be too many different time zones on a continent.
So in 1894, the countries of Europe agreed to synchronize their watches (this means that they show the same time), and to use a unified indication of time. Since then, in continental Europe, with a few exceptions, you no longer have to correct your watch when you pass from one country to another; they all use the same time, which is referred to as Central European Time (CET). This is clearly a great advantage. Nevertheless, back in those days whenh this time reform was first introduced, many sundial owners considered such a time unification to be a real catastrophe!
During recent years, it has been decided to shift the time during the summer period. Thus, each year from spring (late March) to autumn, time used in Central Europe is the Central European Summer Time (CEST) which is equal to Central European Time plus 1 hour.
Similar changes are made in many other regions of the Earth. In 1998, the time will change back to CES in late October. In earlier years, the summer time period in Europe ended in late September; during recent years, the period of summertime has been prolonged by one month.
Sundials work according to astronomical concepts, and before this time unification, the Sun passed the meridian of for instance Barcelona and Stockholm at exactly 12 o'clock local time - per definition.
However, after the introduction of Unified Time, in Stockholm the Sun no longer passes the meridian at exactly 12 o'clock. For instance, on May 01, 1998, the sun passes south as follows:
Stockholm : at 1045 GMT
Barcelona : at 1149 GMT
Greenwich : at 1158 GMT.
It is no wonder, that many sundial owners felt that their sundials lost any relation to reality when this reform was made just over 100 years ago. Some of them became rather desperate and there are cases known where they tried to adjust their instrument with a hammer! The results of such desperate actions may still be seen on some European church sundials!
Fortunately, it is not difficult to measure the time of Local Noon. To do so, you find the direction towards the South, and then note the time, when the Sun is seen in this direction. (If you are south of the equator, you must find North in the same way).
You can also of course use a magnetic needle, but that is not very accurate. To obtain a more precise determination, there are better methods, based on measurements of the Sun itself. The important point is that the Sun reaches its highest point in the sky, exactly at Local Noon. At this time, the shadows are the shortest.