For the period between 4th January 2015 and 12th May 2015, the chart below takes the minute-by-minute frequency readings and depicts the percentage of time that the Grid remained within the statutory frequency limits (i.e. between 49.75 Hz and 50.25 Hz). It also shows the percentage of time during which the Grid was above the upper limit and the percentage of time when it was below the lower limit. Unlike the other two charts in this section, this graph is a static "snapshot" and is not updated every couple of days. The next update will likely take place in September 2015.