Excel stores dates as sequential serial numbers internally. The value 1 is understood to be January 1, 1900 at 12:00 AM. The value 2 is January 2, 1900 at 12:00 AM. A value of 1 increases the date by one day. So, 42100 would be equivalent to April 6, 2015 at 12:00 AM. A value of 0.04 increases the date by one hour. So, 42100.04 would be equivalent to April 6, 2015 at 1:00 AM.
Because the date is stored inside Excel in sequential serial numbers, sometimes this means that instead of seeing a date in Grapher, you will see a very large number representing that date. For instance, the spreadsheet may appear as:
The dates in the left column are in serial number format. Grapher will
set the axis to numeric when creating the graph.
To create a graph from this data, click the Graphs | Create | Basic | Line Plot command. Select the data file and click Open. The X axis will be in numeric format.
The X axis is automatically displayed with numbers instead of dates.
After the graph is created, the axis can be converted to dates. To convert the numbers to dates:
- Click on the X Axis 1 in the Object Manager to select it.
- In the Property Manager, click on the Tick Labels tab.
- In the Major Label Text section, check the box next to the Use date/time format option.
- Do not change the Label source. The Label source should remain Automatic in this case.
The axis converts the numbers to dates using the standard serial number format described above. The axis tick mark spacing and tick label format can be altered.
The X axis is changed to display with date/time values.
Occasionally, when switching between columns for the plot, the Use date/time format option will become checked or unchecked at an undesired change. To display the axis with numeric format, uncheck this box. To display the axis with date format, check this box.
Updated September 30, 2016