Create a separate SignificantFiguresUnits context

macros/contexts/contextSignificantFiguresUnits.pl

@@ -0,0 +1,41 @@
+
+BEGIN { strict->import }
+
+loadMacros('contextUnits.pl', 'contextSignificantFigures.pl');
+
+sub _contextSignificantFiguresUnits_init {
+	context::SignificantFiguresUnits::Init(@_);
+}
+
+package context::SignificantFiguresUnits::NumberWithUnit;
+our @ISA = ('context::Units::NumberWithUnit');
+
+# call the postprocess for handling error messages and flags. 
+# This needs to be called for the SignificantFigure and Units separately. 
+
+sub cmp_postprocess {
+	my ($self, $ansHash) = @_;
+	$self->unit->cmp_postprocess($ansHash);
+
+	# Since the current $ansHash has the correct and student value as the NumberWithUnits type
+	# pass in just the number (SignificantFigure) to the postprocess. 
+	$ansHash->{correct_value} = $ansHash->{correct_value}->number;
+	$ansHash->{student_value} = $ansHash->{student_value}->number;
+	$self->number->cmp_postprocess($ansHash);
+}
+
+package context::SignificantFiguresUnits;
+
+sub Init {
+	my $context = $main::context{SignificantFiguresUnits} = context::Units::extending('SignificantFigures');
+	$context->{value}{NumberWithUnit}     = 'context::SignificantFiguresUnits::NumberWithUnit';
+	$context->{value}{'Number-with-Unit'} = 'context::SignificantFiguresUnits::NumberWithUnit';
+	$context                              = $main::context{LimitedSignificantFiguresUnits} = $context->copy;
+	$context->{name}                      = 'LimitedSignificantFiguresUnits';
+	$context->parens->undefine('|', '{', '[');
+	$context->variables->remove('x');
+	$context->operators->undefine('-', '+', '/', '//', ' /', '/ ', '!', '_', '.', 'U', '><');
+	$context->flags->set(limitedSigFigs => 1);
+}
+
+1;

t/contexts/significant_figures_units.t

@@ -42,4 +42,65 @@ subtest 'Test a number with length units and significant figures' => sub {
 	ok $a == Compute('4.036 ft'), 'Value in feet (a little off, but when converted to m is correct)';
 };
 
+subtest 'Test an actual problem' => sub {
+
+	my $source = <<~'END_SOURCE';
+		DOCUMENT();
+
+		loadMacros("PGstandard.pl","PGML.pl",'contextSignificantFiguresUnits.pl');
+
+		Context('SignificantFiguresUnits')->withUnitsFor('mass');
+
+		Context()->flags->set(
+					tolerance                   => 0.01,
+					partial_incorrect_sf        => 0.6,
+					partial_sf_within_tolerance => 0.8,
+					);
+
+		$a = Compute("123.0 g");
+		$b = Compute("45.3 g");
+		$c = $a+$b;
+
+		BEGIN_PGML
+		A lab technician has a beaker with [$a] of water.  She adds [$b] to the beaker.  Using the proper number of significant figures, what is the total amount in the beaker? 
+
+		[_]{$c}
+		END_PGML
+
+		ENDDOCUMENT();
+	END_SOURCE
+
+	ok my $pg = WeBWorK::PG->new(
+		r_source       => \$source,
+		inputs_ref     => { AnSwEr0001 => '168.3 g' },
+		processAnswers => 1
+		),
+		'source string renders';
+
+	is $pg->{result}{score}, 1, 'correct answer is scored correctly';
+
+	my $pg2 = WeBWorK::PG->new(
+		r_source       => \$source,
+		inputs_ref     => { AnSwEr0001 => '168.30 g' },
+		processAnswers => 1
+	);
+
+	is $pg2->{result}{score}, 0.6, 'check deduction for wrong number of significant figures.';
+	like $pg2->{answers}{AnSwEr0001}{ans_message}, qr/Incorrect number of significant figures/,
+		'Answer processed showing message.';
+
+	my $pg3 = WeBWorK::PG->new(
+		r_source       => \$source,
+		inputs_ref     => { AnSwEr0001 => '168.2 g' },
+		processAnswers => 1
+	);
+
+	is $pg3->{result}{score}, 0.8,
+		'check deduction for right number of significant figures, but answer within tolerance.';
+	like $pg3->{answers}{AnSwEr0001}{ans_message},
+		qr/Correct number of significant figures, but the value is not correct/,
+		'Answer processed showing message.';
+
+};
+
 done_testing;