With digital storage oscilloscopes, the record length determines the number of samples that are measured. All these samples can be measured after the trigger has occurred. It is however possible to measure (a part of) the record before the trigger occurs, by selecting pre samples.
The total record will then be divided in a pre trigger part and a post trigger part, respectively containing pre samples and post samples. This way it is possible to "look back in time" since the pre samples were captured before the trigger moment.
With the TiePie engineering instruments it's possible to define the trigger moment at any position in the record.
Changing the trigger moment in the Multi Channel oscilloscope software can be done in various different ways:
When setting the trigger moment through a popup menu, the option User defined... also allows to set the value as a number of samples or as a time.