diff --git a/rnaseq/umi/07_remove_dups.pl b/rnaseq/umi/07_remove_dups.pl
index 94f3acc..2aa2859 100644
--- a/rnaseq/umi/07_remove_dups.pl
+++ b/rnaseq/umi/07_remove_dups.pl
@@ -1,7 +1,7 @@
 #!/usr/bin/perl -w
 use strict;
 use Parallel::ForkManager;
-
+# this script creats one file with UMI unique reads and one with UMI duplicated reads
 my @torun = ();
 foreach my $file ( <*Aligned.sortedByCoord.out.bam> ) {
     push @torun, $file;
@@ -27,9 +27,9 @@ foreach my $file ( @torun ) {
             next;
         }
         my ( $id, $flag, $chr, $pos, $mapq, $cigar, $chr2, $pos2, $tlen ) = split /\t/;
-        next if $flag & 256 or $flag & 512 or $flag & 1024;
+        next if $flag & 256 or $flag & 512 or $flag & 1024; #skip if the read is not primary alignment/read fails platform/vendor quality checks/read is PCR or optical duplicate
 #        foreach ( 256, 512, 1024 ) { $flag-=$_ if $flag&$_ }
-        my ( $bc ) = $id =~ m/\:([GATCN\d]+)$/;
+        my ( $bc ) = $id =~ m/\:([GATCN\d]+)$/; #extract UMI barcode
         my $uniq = join( ':', $chr, $pos, $flag, $tlen, $bc );
         my $pos_ = $pos-1;
         while ( $cigar =~ m/(\d+)([SHMDIN=])/g ) {