diff --git a/lib/sync64.f90 b/lib/sync64.f90
index d927af9c9..f6d438e32 100644
--- a/lib/sync64.f90
+++ b/lib/sync64.f90
@@ -5,14 +5,14 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
 
   parameter (NMAX=60*12000)                  !Max size of raw data at 12000 Hz
   parameter (NSPS=3456)                      !Samples per symbol at 6000 Hz
-  parameter (NSPC=7*NSPS)                    !Samples per Costas array
+  parameter (NSPC=7*NSPS)                    !Samples per Costas waveform
   real s1(0:NSPC-1)                          !Power spectrum of Costas 1
   real s2(0:NSPC-1)                          !Power spectrum of Costas 2
   real s3(0:NSPC-1)                          !Power spectrum of Costas 3
   real s0(0:NSPC-1)                          !Sum of s1+s2+s3
   real s0a(0:NSPC-1)                         !Best synchromized spectrum (saved)
   real s0b(0:NSPC-1)                         !tmp
-  real a(5)
+  real a(5)                                  !Parameters of Lorentzian fit
   integer icos7(0:6)                         !Costas 7x7 tones
   integer ipk0(1)
   complex cc(0:NSPC-1)                       !Costas waveform
@@ -25,11 +25,12 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
   save
 
   if(mode64.ne.mode64z) then
+! Submode has changed, recompute the complex Costas waveform
      twopi=8.0*atan(1.0)
      dfgen=mode64*12000.0/6912.0
      k=-1
      phi=0.
-     do j=0,6                               !Compute complex Costas waveform
+     do j=0,6
         dphi=twopi*10.0*icos7(j)*dfgen/6000.0
         do i=1,NSPS
            phi=phi + dphi
@@ -42,7 +43,6 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
   endif
 
   nfft3=NSPC
-  nh3=nfft3/2
   df3=6000.0/nfft3
   
   fa=max(nf1,nfqso-ntol)
@@ -61,7 +61,7 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
   smaxall=0.
   jpk=0
   ja=0
-  jb=(5.0+emedelay)*6000
+  jb=(5.0+emedelay)*6000                 !Bigger range than necessary?
   jstep=100
   ipk=0
   kpk=0
@@ -69,7 +69,7 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
   if(mod(nadd,2).eq.0) nadd=nadd+1       !Make nadd odd
   nskip=max(49,nadd)
 
-  do j1=ja,jb,jstep
+  do j1=ja,jb,jstep                      !Loop over DT
      call timer('sync64_1',0)
      j2=j1 + 39*NSPS
      j3=j1 + 77*NSPS
@@ -95,7 +95,7 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
      s0(ia:ib)=s1(ia:ib) + s2(ia:ib) + s3(ia:ib)
      s0(:ia-1)=0.
      s0(ib+1:)=0.
-     if(nadd.ge.3) then
+     if(nadd.ge.3) then                    !Smooth the spectrum
         do ii=1,3
            s0b(ia:ib)=s0(ia:ib)
            call smo(s0b(ia:ib),iz,s0(ia:ib),nadd)
@@ -114,7 +114,7 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
         f0=ip*df3
      endif
      call timer('sync64_2',1)
-  enddo
+  enddo  ! j1 (DT loop)
 
   s0a=s0a+2.0
 !  write(17) ia,ib,s0a(ia:ib)                !Save data for red curve
@@ -141,7 +141,6 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
   rewind 17
   write(17,1110) 0.0,0.0
   rewind 17
-!  rewind 76
   do i=2,iz-2*nskip-1,3
      x=i
      z=(x-a(3))/(0.5*a(4))
@@ -155,11 +154,9 @@ subroutine sync64(c0,nf1,nf2,nfqso,ntol,mode64,emedelay,dtx,f0,jpk,sync,  &
      ss=(s0a(j-1)+s0a(j)+s0a(j+1))/3.0
      if(ss.gt.slimit) write(17,1110) freq,ss
 1110 format(3f10.3)
-!     write(76,1110) freq,ss,yfit
   enddo
   flush(17)
   close(17)
-!  flush(76)
 
   return
 end subroutine sync64