### Sidebar

public:vievs_manual:exercises_clock_break

# Clock break

In this exercise a clock break at a station clock has to be corrected by the user. The station at which a clock break occurs should not be taken as a reference clock (see the Chapter about Opt files on how to change the reference clock).

A typical residual plot of a session with a clock break is depicted in the Figure below: Large residuals are close together at a certain epoch.

To find the station and epoch of the clock break, the user can go to Plotting - Residuals, select the output subfolder of the processed session and click Load. When the session is selected in the second popup-menu, the residuals appear in the plot window. Select First to show only the first-solution (only one zenith wet delay and one clock function per station is estimated) and Station to see only the residuals of one station. The two Figures below depict the residuals of two different stations for a session with a clock break. The clock break occurs at ZELENCHK (upper figure) since the jump in residuals can be seen in all observations (to all other stations).

To remove the clock break (or in other words: add clock break information) we click on the button Add clock break - a grey cross-wire appears - and the user clicks on the epoch of the 'vertical' line of the clock break (the y-value is not important). To make it easier, the user can zoom in before clicking on Add clock break (see Figure below). When zooming is finished, deselect the zooming again!

The clock break information will be written to the OPT file in the folder selected in File - Set input files. The clock break information will be applied the next time VieVS processes this session (when the same OPT-folder is selected).

| <= back |