All times are stored inside the QViewer, QEditor, and timeline files as numbers relative to midnight on 1 January 1970 UTC. All days are assumed to be exactly the same length.
The QViewer's display time is printed in the datetime box. In order to print the date and time and to parse dates and times the user types in this box, the QViewer needs to know the timezone and calendar in use. When the QViewer application starts, it reads the timezone from the operating system and reads the calendar from its own list of user preferences. The timezone name next to the display time is on a button. Choosing the button presents a dialog that allows the user to set the timezone and calendar to new values. The initial calendar can be changed by editing the defaultCalendar variable in the common section of the edit preference window.
The display time is a single plane (the front clipping plane), perpendicular to the time axis, that clips off events when the view direction is facing toward the future or the past along the time axis. When the view direction is facing left or right along the x axis, the display time is represented as a faint vertical line on the center of the display area. Times before the display time are on one side of the line and after the display time on the other.
|Side view with the thin center line representing the display time. The timeline shows the uncertainty about Shakespeare's birth date.|
Sometimes the exact start or end times of events are known only to be within a certain range. In this case, the author of a timeline can give a nominal time and a range forward and backward from that time. When drawing these events as the standard open-ended box, the QViewer will allow the edge to fade or become more transparent to represent the accuracy range.
|Supreme Court justices showing the uncertainty of the ends of the terms of the current members. The upper range of the uncertainty is based on the longest historical term of a justice.|
Events that continue into the future may have an indefinite end time. The author can choose to represent this situation by assigning an open duration to the end of the event. This is shown in the QViewer as an event time that gradually fades from the present time to the end of the duration. Conscientious authors will use one of these mechanisms rather than assign an arbitrary end time very far in the future.
The QViewer completely ignores the relativistic nature of spacetime by assuming there is a single time in the QViewer's imaginary space for each point along the time axis and that durations that start and end at the same points on the time axis are equal. This limitation becomes more apparent when timelines represent actions of objects moving in relation to each other at high speed or at small time scales.
The clock time is the date and time that the QViewer reads from the machine's operating system and represents, at some level of precision and accuracy, the time on standard clocks outside the user's machine. The display time is set to the present clock time when the QViewer program starts. The set time to clock time and reset commands both set the display time to the present clock time.