var.diff=function(data,y,N){ 
  data=as.name(data)
  n=length(y)
  ybar.sd=mean(y); d=diff(y)
  d2i=sum(d^2); fpc=(1-n/N)
  vhat.sd=fpc*(1/(2*(n-1)))*(d2i/n)
  bound=2*sqrt(vhat.sd)
  lower=ybar.sd-bound; upper=ybar.sd+bound
  cat("","\n","Results of Successive Difference calculations",'\n',"Data =",data," N =",
      N," n =",n,"\n", "FPC =",fpc,"\n", "Estimate of mean =",ybar.sd,"\n","Vhat =", vhat.sd,"\n",
      "Bound =",bound,"\n","Lower Bound =",lower, "Upper Bound =",upper,"\n")
  results=list(data=data,ybar.sd=ybar.sd,vhat.sd=vhat.sd,N=N,n=n,fpc=fpc,lower=lower,upper=upper)
}
# to use the function with its call:
# var.diff(data,y,N)

# data: name of dataset, in quotes
# y: vector (data)
# N: population size