When the X-axis is set to style ‘Date’, ‘Annual’ or ‘Monthly’, the date labels may be formatted with a simple picture format such as:

chSet 'dpic' 'MMM-yy'

To label the tickmarks ‘Jan-01’ ‘Feb-01’ .... ‘Dec 02’ as appropriate. The months will be shown in your local language.

The date specification in detail
The following table is taken from the Microsoft documentation for the GetDateFormat API call, and is common to all Windows applications which use it:

Picture	Meaning
d	Day of month as digits with no leading zero for single-digit days.
dd	Day of month as digits with leading zero for single-digit days.
ddd	Day of week as a three-letter abbreviation. The function uses the LOCALE_SABBREVDAYNAME value associated with the specified locale.
dddd	Day of week as its full name. The function uses the LOCALE_SDAYNAME value associated with the specified locale.
M	Month as digits with no leading zero for single-digit months.
MM	Month as digits with leading zero for single-digit months.
MMM	Month as a three-letter abbreviation. The function uses the LOCALE_SABBREVMONTHNAME value associated with the specified locale.
MMMM	Month as its full name. The function uses the LOCALE_SMONTHNAME value associated with the specified locale.
y	Year as last two digits, but with no leading zero for years less than 10.
yy	Year as last two digits, but with leading zero for years less than 10.
yyyy	Year represented by full four digits.

Any text that should remain in its exact form in the date string should be enclosed within single quotation marks in the date format picture. The single quotation mark may also be used as an escape character to allow the single quotation mark itself to be displayed in the date string. However, the escape sequence must be enclosed within two single quotation marks. For example, to display the date as “May ‘93”, the format string would be: “MMMM ‘’’’yy” The first and last single quotation marks are the enclosing quotation marks. The second and third single quotation marks are the escape sequence to allow the single quotation mark to be displayed before the century.

See also ...
Locale – for formatted dates or times