diff --git a/NEWS b/NEWS
index 446769524..846bda49d 100644
--- a/NEWS
+++ b/NEWS
@@ -6,11 +6,18 @@ New in spot 2.1.2.dev (not yet released)
     LTL over finite words) model checking to LTL model checking.  This
     is based on a transformation by De Giacomo & Vardi (IJCAI'13).
 
+  * "ltldo --stats=%R", which used to display the serial number of the
+    formula processed, was renamed to "ltldo --stats=%#" to free %R
+    for the following feature.
+
   * autfilt, dstar2tgba, ltl2tgba, ltlcross, ltldo learned to time any
-    task in a more precise way thanks to %R, %[LETTER]R option. User time,
-    system time or children processing time or ... (see --help) can be
-    measured separately. A typical use-case is to exclude time spent
-    inside ltldo by keeping only time spent in each executed tool.
+    task in a more precise way thanks to %R, %[LETTER]R option. User
+    or system time, for children or parent, can be measured
+    separately.  A typical use-case is "ltldo --stats='... %[c]R ...'
+    ..." to measure the time spent in the tool ran by ltldo, excluding
+    that of ltldo.  In all tools, the difference between %r
+    (wall-clock time) and %R (process time) can also be used to detect
+    unreliable measurements.
 
   Library:
 
diff --git a/bin/ltldo.cc b/bin/ltldo.cc
index 81cc3da33..1664704ae 100644
--- a/bin/ltldo.cc
+++ b/bin/ltldo.cc
@@ -66,7 +66,7 @@ static const argp_option options[] =
 
 static const argp_option more_o_format[] =
   {
-    { "%R", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
+    { "%#", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "serial number of the formula translated", 0 },
     { "%T", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "tool used for translation", 0 },
@@ -262,7 +262,7 @@ namespace
       : runner(dict), post(post)
     {
       printer.add_stat('T', &cmdname);
-      printer.add_stat('R', &roundval);
+      printer.add_stat('#', &roundval);
       printer.add_stat('f', &inputf);
     }
 
diff --git a/tests/core/ltldo.test b/tests/core/ltldo.test
index c005288e9..5dab1e4a3 100755
--- a/tests/core/ltldo.test
+++ b/tests/core/ltldo.test
@@ -53,7 +53,7 @@ test "`echo 1,a,3,4 | ltldo -F-/2 ltl2tgba --stats='%<,%s,%>'`" = '1,2,3,4'
 
 $genltl --and-gf=1..3 |
 run 0 $ltldo "{tgba}$ltl2tgba %f -H >%H" "{ba}$ltl2tgba >%N %f -s" \
-	     --stats="%T,%R,%f,%s,%t,%e" >output
+	     --stats="%T,%#,%f,%s,%t,%e" >output
 cat output
 cat >expected <<EOF
 tgba,1,GFp1,1,2,2
@@ -146,3 +146,9 @@ grep ':.*empty input' stderr
 
 $ltldo '{name} foo/bar/ltl2baextended' -f GFa 2>stderr && exit 1
 grep 'error:.*foo/bar/ltl2baextended -f .*>.*' stderr
+
+
+genltl --rv-counter=9 | ltldo ltl2tgba --stats='
+print("%[up]R + %[uc]R + %[sp]R + %[sc]R - %R\n");
+die if abs(%[up]R + %[uc]R + %[sp]R + %[sc]R - %R) > 0.02;' > code.pl
+perl code.pl