diff --git a/Models/Instruments/PFD/PFD.nas b/Models/Instruments/PFD/PFD.nas
index aa26b172..424c3323 100644
--- a/Models/Instruments/PFD/PFD.nas
+++ b/Models/Instruments/PFD/PFD.nas
@@ -19,6 +19,7 @@ var ASItrgtdiff = 0;
 var ASImax = 0;
 var ASItrend = 0;
 var altTens = 0;
+var altPolarity = "";
 
 # Fetch nodes:
 var state1 = props.globals.getNode("/systems/thrust/state1", 1);
@@ -807,7 +808,12 @@ var canvas_PFD_base = {
 		me["ALT_two"].setText(sprintf("%03d", abs(me.middleAltText-5)));
 		me["ALT_one"].setText(sprintf("%03d", abs(me.middleAltText-10)));
 		
-		me["ALT_digits"].setText(sprintf("%s", altitude_pfd.getValue()));
+		if (altitude.getValue() < 0) {
+			altPolarity = "-";
+		} else {
+			altPolarity = "";
+		}
+		me["ALT_digits"].setText(sprintf("%s%d", altPolarity, altitude_pfd.getValue()));
 		altTens = num(right(sprintf("%02d", altitude.getValue()), 2));
 		me["ALT_tens"].setTranslation(0, altTens * 1.392);
 		
diff --git a/Nasal/libraries.nas b/Nasal/libraries.nas
index cf748ebf..67d5ec48 100644
--- a/Nasal/libraries.nas
+++ b/Nasal/libraries.nas
@@ -276,7 +276,7 @@ setlistener("/options/steep-ils", func {
 
 canvas.Text._lastText = canvas.Text["_lastText"];
 canvas.Text.setText = func(text) {
-	if (text == me._lastText) {return me;}
+	if (text == me._lastText and text != nil and size(text) == size(me._lastText)) {return me;}
 	me._lastText = text;
 	me.set("text", typeof(text) == 'scalar' ? text : "");
 };
diff --git a/Systems/libraries.xml b/Systems/libraries.xml
index 9cfa1f88..5d635c95 100644
--- a/Systems/libraries.xml
+++ b/Systems/libraries.xml
@@ -90,7 +90,7 @@
 		<input>
 			<expression>
 				<table>
-					<property>/engines/engine[0]/n2-actual</property> 
+					<property>/engines/engine[0]/n2-actual</property>
 					<entry><ind>11</ind><dep> 2</dep></entry>
 					<entry><ind>58</ind><dep>48</dep></entry>
 				</table>
@@ -107,7 +107,7 @@
 		<input>
 			<expression>
 				<table>
-					<property>/engines/engine[1]/n2-actual</property> 
+					<property>/engines/engine[1]/n2-actual</property>
 					<entry><ind>11</ind><dep> 2</dep></entry>
 					<entry><ind>58</ind><dep>48</dep></entry>
 				</table>
@@ -125,7 +125,7 @@
 			<expression>
 				<floor>
 					<div>
-						<property>/instrumentation/altimeter/indicated-altitude-ft</property> 
+						<abs><property>/instrumentation/altimeter/indicated-altitude-ft</property></abs>
 						<value>100</value>
 					</div>
 				</floor>
@@ -143,7 +143,7 @@
 				<floor>
 					<div>
 						<abs>
-							<property>/it-autoflight/internal/vert-speed-fpm</property> 
+							<property>/it-autoflight/internal/vert-speed-fpm</property>
 						</abs>
 						<value>100</value>
 					</div>
@@ -372,7 +372,7 @@
 		<name>Outflow Valve</name>
 		<type>noise-spike</type>
 		<input>
-			<property>/systems/pressurization/outflowpos</property> 
+			<property>/systems/pressurization/outflowpos</property>
 		</input>
 		<output>/systems/pressurization/outflowpos-norm</output>
 		<max-rate-of-change>1</max-rate-of-change>
@@ -408,7 +408,7 @@
 		<name>Cabin VS</name>
 		<type>noise-spike</type>
 		<input>
-			<property>/systems/pressurization/vs</property> 
+			<property>/systems/pressurization/vs</property>
 		</input>
 		<output>/systems/pressurization/vs-norm</output>
 		<max-rate-of-change>500</max-rate-of-change>
@@ -442,7 +442,7 @@
 		<input>
 			<expression>
 				<table>
-					<property>/it-autoflight/internal/vert-speed-fpm</property> 
+					<property>/it-autoflight/internal/vert-speed-fpm</property>
 					<entry><ind>-50000</ind><dep> -750</dep></entry>
 					<entry><ind> -2000</ind><dep> -750</dep></entry>
 					<entry><ind> -1000</ind><dep> -250</dep></entry>
@@ -468,7 +468,7 @@
 		<input>
 			<expression>
 				<table>
-					<property>/systems/pressurization/outflowpos-man</property> 
+					<property>/systems/pressurization/outflowpos-man</property>
 					<entry><ind>0.0</ind><dep>-1000</dep></entry>
 					<entry><ind>0.5</ind><dep>    0</dep></entry>
 					<entry><ind>1.0</ind><dep> 2500</dep></entry>
@@ -555,7 +555,7 @@
 		<input>
 			<expression>
 				<table>
-					<property>fdm/jsbsim/inertia/weight-kg</property>  <!-- from FCOM vol 3 page 613 -->
+					<property>fdm/jsbsim/inertia/weight-kg</property> <!-- from FCOM vol 3 page 613 -->
 					<entry><ind>160000</ind><dep>40500</dep></entry>
 					<entry><ind>165000</ind><dep>40000</dep></entry>
 					<entry><ind>170000</ind><dep>39500</dep></entry>
diff --git a/revision.txt b/revision.txt
index 3084ff19..175c1b51 100644
--- a/revision.txt
+++ b/revision.txt
@@ -1 +1 @@
-4724
\ No newline at end of file
+4725
\ No newline at end of file