MetaStock -> Tools -> Indicator Builder -> New
Copy and paste formula below.


====================
Calendar Day counter
====================
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{Day counter from 1/1/0001, Gregorian calendar.
 Count is independent of any missing chart data.

 Copyright © 2003-2007 Jose Silva.
 The grant of this license is for personal use
  only - no resale or repackaging allowed.
 All code remains the property of Jose Silva.
 http://www.metastocktools.com }

{ User input }
limit:=Input("count calendar days from year",1,2200,2000);

{ Day counter }
LimLeap:=Frac(limit/4)=0 AND Frac(limit/100)<>0
 OR Frac(limit/400)=0;
NoCount:=limit*365+Int(limit/4)
 -Int(limit/100)+Int(limit/400)-LimLeap;
leap:=Frac(Year()/4)=0 AND Frac(Year()/100)<>0
 OR Frac(Year()/400)=0;
y:=Year()*365+Int(Year()/4)
 -Int(Year()/100)+Int(Year()/400)-NoCount;
m:=
 If(Month()=2,31-leap,
 If(Month()=3,59,
 If(Month()=4,90,
 If(Month()=5,120,
 If(Month()=6,151,
 If(Month()=7,181,
 If(Month()=8,212,
 If(Month()=9,243,
 If(Month()=10,273,
 If(Month()=11,304,
 If(Month()=12,334,
 -leap)))))))))));
DayNr:=y+m+DayOfMonth();

{ Plot in own window }
DayNr

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