CALENDAR
The date may be set either manually or by clicking on a increment button. The month will increment through December to January and the other way, and also change the year to the correct value. If either a new month is selected or a new year is typed in the box, one must click the Get Date button. The Today button returns the Calendars to the original display. Years below 1583 are not allowed due to the calendar change that took place in 1582.
There are comments in the code to change the display so that the current month is last or first, set the number displayed rather than asking and set the number across (set for 4 now).

DIFFERENCE
The two dates may be set manually or by clicking on a calendar.  The first click will set the first date and the next click the To date, and alternate afterwards. Clicking the Now button on either date will set that date to today. Clicking Get Diff will give the number of calendar days between the two dates, either positive or negative, regardless of DST differences.

JULIAN
Returns the Julian date for the first date at 12 noon UTC.  This is the time the Julian day turns rather than at midnight so this is the afternoon-evening Julian date.

ADJUST
The days, + or -, in the text area are added to the first date above and the result is shown in the display box below. Time is set for 12 noon am of the date above; answer date indicates hour difference due to DST.