--- loncom/homework/caparesponse/caparesponse.pm	2016/08/09 23:43:45	1.258
+++ loncom/homework/caparesponse/caparesponse.pm	2018/09/13 17:00:05	1.259
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # caparesponse definition
 #
-# $Id: caparesponse.pm,v 1.258 2016/08/09 23:43:45 raeburn Exp $
+# $Id: caparesponse.pm,v 1.259 2018/09/13 17:00:05 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -664,7 +664,14 @@ sub end_numericalresponse {
 	my (@formats)=&Apache::lonxml::get_param_var('format',$parstack,$safeeval);
 
 	my $unit=&Apache::lonxml::get_param_var('unit',$parstack,$safeeval);
-	
+	my ($needsdollar,$needscomma);
+	if ($unit =~ /\$/) {
+	    $needsdollar = 1;
+	}
+	if ($unit =~ /\,/) {
+	    $needscomma = 1;
+	}
+
 	if ($target eq 'answer') {
 	    $result.=&Apache::response::answer_header($tag,undef,
 						      scalar(keys(%answer)));
@@ -760,7 +767,7 @@ sub end_numericalresponse {
 			if ($unit=~/\,/) { $fmt="\,".$fmt; $unit=~s/\,//g; }
 			$element = &format_number($element,$fmt,$target,
 						  $safeeval);
-			if ($fmt=~/\$/ && $unit!~/\$/) { $element=~s/\$//; }
+			if ($fmt=~/\$/ && !$needsdollar) { $element=~s/\$//; }
 		    }
 		}
 		push(@fmt_ans,join(',',@$ans));
@@ -773,7 +780,7 @@ sub end_numericalresponse {
 		! ($Apache::lonhomework::type eq 'exam' ||
 		   lc($hideunit) eq "yes") )  {
 		my $cleanunit=$unit;
-		$cleanunit=~s/\$\,//g;
+		$cleanunit=~s/[\$,]//g;
 		foreach my $ans (@fmt_ans) {
 		    $ans.=" $cleanunit";
 		}
@@ -790,7 +797,13 @@ sub end_numericalresponse {
 						    $tag,$parstack,
 						    $safeeval,1);
 		    $error=&mt("Computer's answer is incorrect ([_1]).",'"'.join(', ',@$response).'"').' ';
-                    if ($ad eq 'UNIT_INVALID_STUDENT') {
+                    if (($ad eq 'NO_UNIT') && $needsdollar) {
+                        $error.=&mt('The unit attribute includes [_1] but the answer format does not.','$').' '.
+                                &mt('Either remove the [_1] from the unit or prepend [_1] to the answer format.','$');    
+                    } elsif (($ad eq 'COMMA_FAIL') && $needscomma) {
+                        $error.=&mt('The unit attribute includes [_1] but the answer format does not.',',').' '.
+                                &mt('Either remove the [_1] from the unit or prepend [_1] to the answer format.',',');
+                    } elsif ($ad eq 'UNIT_INVALID_STUDENT') {
                         $error.=&mt('Unable to interpret units. Computer reads units as "[_1]".',$msg).' '.
                                 &mt('The unit attribute in the numericalresponse item needs to be a supported physical unit.');
 		    } elsif ($sigline ne '') {