diff --git a/backup b/backup
index a2278de..b8a7794 100755
--- a/backup
+++ b/backup
@@ -1,8 +1,19 @@
 #!/bin/bash
 # James W. Barnett
 
+# Takes snapshots of each snapper configuration. It then sends the snapshot to
+# a location on an external drive. After the initial transfer, it does
+# incremental snapshots on later calls. It's important not to delete the
+# snapshot created on your system since that will be used to determine the
+# difference for the next incremental snapshot.
+
+# Can set the backup directory here, or in the snapper configuration file with
+# EXT_BACKUP_LOCATION
 declare -r mybackupdir="/run/media/wes/backup/acer-c720"
 
+# You can set a snapper configuration to be excluded by setting EXT_BACKUP="no"
+# in its snapper configuration file.
+
 #--------------------------------------------------------
 # Don't modify anything below here
 
@@ -15,8 +26,11 @@ fi
 
 declare -r description="latest incremental backup"
 
-# It's important not to change this userdata in the snapshots.
-declare -r userdata="extbackup=yes"
+# It's important not to change this userdata in the snapshots, since that's how
+# we find the previous one.
+UUID="$(blkid -L backup | awk -F'/' '{print $4}')"
+declare -r userdata="uuid=$UUID"
+#declare -r userdata="extbackup=yes"
 declare -r configs="$(find /etc/snapper/configs/* -printf '%f\t\0')"
 
 for x in $configs; do
@@ -32,6 +46,9 @@ for x in $configs; do
         if [[ -z $BACKUPDIR ]]; then
             echo "ERROR: External backup location not set!"
             exit 1
+        elif [[ ! -d $BACKUPDIR ]]; then
+            echo "ERROR: $BACKUPDIR is not a directory."
+            exit 1
         fi
 
         old_number=$(snapper -c $x list -t single | awk '/'"$userdata"'/ {print $1}')
@@ -50,10 +67,6 @@ for x in $configs; do
             echo "Performing initial backup for snapper configuration '$x'. This could take awhile..."
             btrfs send $new_snapshot | btrfs receive $backup_location
 
-            echo "The latest incremental backup snapshot for snapper configuration '$x' "
-            echo "is $new_number. Do not delete this snapshot, or you when you run this "
-            echo "script again, it will send ALL data again, not just the incremental change. "
-
         else
 
             old_snapshot=$SUBVOLUME/.snapshots/$old_number/snapshot