program define dtdiff
version 2.1
	if "%_*"=="" { 
		di in red "invalid syntax -- see help dtdiff"
		exit 198
	}
	if "%_2"=="" { dtdiff }
	if _N != 0 { 
		di in red "no; data in memory would be lost" 
		exit 4
	}
	quietly set obs 1
	gen DATE1=%_1
	gen DATE2=%_2
	ftoe DATE1, gen(JDATE1)
	ftoe DATE2, gen(JDATE2)
*
* Assumes last day is not included in spell ("to, not "through")
*
	di
	di "Difference in Days is:   " %7.0f = (JDATE2-JDATE1)
	di "Difference in Weeks is:  " %7.2f = (JDATE2-JDATE1)/7
	di "Difference in Years is:  " %7.3f = (JDATE2-JDATE1)/365.25
	drop _all
end