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


=============
EMA - slope %
=============
---8<---------------------------

{ EMA slope % v2.0, +/- 0~100% }
{ ©Copyright 2003 Jose Silva }
{ http://www.metastocktools.com }

pds:=Input("EMA periods",2,2520,21);
x:=Input("use Open=1 High=2 Low=3 Close=4 Volume=5 P=6",1,6,4);

x:=If(x=1,O,If(x=2,H,If(x=3,L,If(x=5,V,If(x=6,P,C)))));
EMA:=Mov(x,pds,E);
EMAprev:=Ref(EMA,-1);

y:=Min(EMA,EMAprev)/Max(EMA,EMAprev);
EMAratio:=(If(EMA>EMAprev,2-y,y)-1)*100;
EMAper:=If(EMAratio<0,Atan(EMAratio,1)-360,
 Atan(EMAratio,1))*10/9;
signal:=Mov(EMAper,pds,E);

0;signal;EMAper

---8<---------------------------


http://www.metastocktools.com