real function covar(x,y)
      real x,y
      include 'nt.inc'
      real sum,sumx,sumy,sumxx,sumyy,sumxy
      common /covarc/sum,sumx,sumy,sumxx,sumyy,sumxy
      if (ichevt.eq.1) then
        sum=0
        sumx=0
        sumy=0
        sumxx=0
        sumyy=0
        sumxy=0
      endif
      sum=sum+1
      sumx=sumx+x
      sumy=sumy+y
      sumxx=sumxx+x*x
      sumyy=sumyy+y*y
      sumxy=sumxy+x*y
      covar=1
      end

      subroutine covarep
      real sum,sumx,sumy,sumxx,sumyy,sumxy
      common /covarc/sum,sumx,sumy,sumxx,sumyy,sumxy
      real slope,cept,sigxx,sigyy,sigxy,rho,rms
      sigxx = (sumxx-sumx*sumx/sum)/sum
      sigyy = (sumyy-sumy*sumy/sum)/sum
      sigxy = (sumxy-sumx*sumy/sum)/sum
      slope = sigxy/sigxx
      cept = (sumy-slope*sumx)/sum
      rho = sigxy/sqrt(sigxx*sigyy)
      rms = sqrt((sumyy+slope*slope*sumxx+cept*cept*sum
     +      -2*slope*sumxy-2*cept*sumy+2*slope*cept*sumx)/sum)
      print *, 'Covariance summary report'
      print *, '  total events seen:',sum
      print *, '  linear fit: y =',slope,' x +',cept
      print *, '  correlation:', rho
      print *, '  rms width:', rms
      end