efsinternal series variable

[sunman4008]

Hello,
I want to create a new series variable that uses past values of itself for current calculations. I learned you can create a series by using efsinternal, which is show below. In the testatr function...I want to access previous values of same variable. Does anyone know how to do it?


function testatr()
{
return(atrt);
}

main
{
atrt = efsInternal("testatr");
}