diff --git a/src/core/Integer.ts b/src/core/Integer.ts
index 7d78d79..b9dfe62 100644
--- a/src/core/Integer.ts
+++ b/src/core/Integer.ts
@@ -47,6 +47,10 @@ export class Integer {
         return new Integer(value, 8);
     }
 
+    isTheSame  (other : Integer) : boolean {
+        return this.value == other.value && this.signed == other.signed && this.maxBitSize == other.maxBitSize;
+    }
+
     toUnsigned() {
         return this.signed 
             ? new Integer(BigInt("0b" + this.toString(2)), this.maxBitSize, false)
diff --git a/src/core/calc.test.ts b/src/core/calc.test.ts
index 9cc4692..32284fa 100644
--- a/src/core/calc.test.ts
+++ b/src/core/calc.test.ts
@@ -62,6 +62,13 @@ describe('calc.addSpace', () => {
         expect(calc.addSpace(n16, 1).maxBitSize).toBe(32);
         expect(calc.addSpace(n16, 32).maxBitSize).toBe(64);
     });
+
+    it('preserves the sign when extending number', () => {
+        const byte = Integer.byte(-1);
+        const actual = calc.addSpace(byte, 1);
+        expect(actual.maxBitSize).toBe(16);
+        expect(actual.num()).toBe(-1);
+    })
 });
 
 describe('calc.numberOfBitsDisplayed', () => {
diff --git a/src/core/calc.ts b/src/core/calc.ts
index 9467d77..7a11ad0 100644
--- a/src/core/calc.ts
+++ b/src/core/calc.ts
@@ -1,5 +1,5 @@
 import { Integer, JsNumber,  asInteger } from "./Integer";
-import { asIntN } from "./utils";
+import { asIntN, logLines } from "./utils";
 
 export default {
     abs (num : Integer) : Integer {
@@ -20,9 +20,8 @@ export default {
     },
 
     addSpace(number: Integer, requiredSpace: number) : Integer {
-        const bin = this.toBinaryString(number);
         const totalSpaceRequired = number.maxBitSize + requiredSpace;
-        return new Integer(BigInt("0b" + bin), nextPowOfTwo(totalSpaceRequired));
+        return new Integer(number.value, nextPowOfTwo(totalSpaceRequired));
     },
 
     operation (op1: Integer, operator: string, op2 : Integer) : Integer {
diff --git a/src/core/components/BinaryString.tsx b/src/core/components/BinaryString.tsx
index e477438..6882795 100644
--- a/src/core/components/BinaryString.tsx
+++ b/src/core/components/BinaryString.tsx
@@ -4,10 +4,10 @@ import './BinaryString.css';
 export type BinaryStringViewProps = {
     allowFlipBits?: boolean;
     binaryString: string;
-    onFlipBit?: (input: FlipBitEventArg) => void;
+    onBitClicked?: (input: FlipBitEventArg) => void;
     emphasizeBytes?: boolean;
-    className?:string;
-    disableHighlight?:boolean,
+    className?: string;
+    disableHighlight?: boolean,
     signBitIndex?: number,
 };
 
@@ -15,7 +15,8 @@ export type FlipBitEventArg = {
     bitIndex: number;
     binaryStringLength: number;
     $event: any;
-    newBinaryString: string
+    newBinaryString: any;
+    isTypeExtend: boolean
 };
 
 export default class BinaryStringView extends React.Component<BinaryStringViewProps> {
@@ -23,8 +24,8 @@ export default class BinaryStringView extends React.Component<BinaryStringViewPr
         return <span className={this.props.className}>{this.getChildren()}</span>
     }
 
-    onBitClick(index: number, e : any) {
-        if(!this.props.allowFlipBits || !this.props.onFlipBit) {
+    onBitClick(index: number, isExtra: boolean, e: any) {
+        if (!this.props.allowFlipBits || !this.props.onBitClicked) {
             return;
         }
 
@@ -32,20 +33,26 @@ export default class BinaryStringView extends React.Component<BinaryStringViewPr
         arr[index] = arr[index] == '0' ? '1' : '0';
         const newBinaryString = arr.join('');
 
-        this.props.onFlipBit({ bitIndex: index, binaryStringLength: this.props.binaryString.length, $event: e, newBinaryString });        
+        this.props.onBitClicked({
+            bitIndex: index, 
+            binaryStringLength: this.props.binaryString.length,
+            newBinaryString: newBinaryString, 
+            $event: e,
+            isTypeExtend: isExtra
+        });
     }
 
     getChildren() {
         var bits = this.createBits(this.props.binaryString.split(''));
-        
-        if(this.props.emphasizeBytes) {
+
+        if (this.props.emphasizeBytes) {
             return this.splitIntoBytes(bits);
         }
 
         return bits;
     }
 
-    createBits(bitChars:string[]) : JSX.Element[] {
+    createBits(bitChars: string[]): JSX.Element[] {
         const allowFlipBits = this.props.allowFlipBits || false;
         const css = allowFlipBits ? ' flipable' : ''
 
@@ -56,18 +63,19 @@ export default class BinaryStringView extends React.Component<BinaryStringViewPr
             var className = c == '1' ? `one${css}` : `zero${css}`;
             var tooltip = '';
 
-            if(i < (this.props.signBitIndex || 0))
+            const isExtra = i < (this.props.signBitIndex || 0);
+            if (isExtra)
                 className += ' extra-bit';
 
-            if(i === this.props.signBitIndex) {
+            if (i === this.props.signBitIndex) {
                 className += ' accent1';
                 tooltip = 'Signature bit. 0 means a positive number and 1 means a negative.'
             }
-                
-            if(disableHighlight) 
+
+            if (disableHighlight)
                 className = css;
 
-            return <span className={className} title={tooltip} key={i} onClick={e => this.onBitClick(i, e)}>{c}</span>
+            return <span className={className} title={tooltip} key={i} onClick={e => this.onBitClick(i, isExtra, e)}>{c}</span>
         });
     }
 
@@ -75,10 +83,10 @@ export default class BinaryStringView extends React.Component<BinaryStringViewPr
         const bytes = [];
 
         var key = 0;
-        while(bits.length > 0) {
+        while (bits.length > 0) {
             bytes.push(<span key={key++} className="byte">{bits.splice(0, 8)}</span>);
         }
-        
+
         return bytes;
     }
 }
\ No newline at end of file
diff --git a/src/expression/components/BitwiseResultView.tsx b/src/expression/components/BitwiseResultView.tsx
index 0cc88cd..63a720e 100644
--- a/src/expression/components/BitwiseResultView.tsx
+++ b/src/expression/components/BitwiseResultView.tsx
@@ -1,6 +1,6 @@
 import React from 'react';
 import formatter from '../../core/formatter';
-import BinaryStringView, { FlipBitEventArg } from '../../core/components/BinaryString';
+import BinaryStringView, { FlipBitEventArg as BitClickedEventArg } from '../../core/components/BinaryString';
 import BitwiseResultViewModel from './BitwiseResultViewModel';
 import { Expression, ExpressionElement } from '../expression-interfaces';
 import { Operator, Operand, ListOfNumbers } from '../expression';
@@ -8,6 +8,7 @@ import calc from '../../core/calc';
 import { Integer } from '../../core/Integer';
 import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';
 import { faUndo } from '@fortawesome/free-solid-svg-icons';
+import loglevel from 'loglevel';
 
 type BitwiseResultViewProps = {
     expression: Expression;
@@ -72,10 +73,11 @@ export default class BitwiseResultView extends React.Component<BitwiseResultView
                 emphasizeBytes={this.props.emphasizeBytes}
                 maxNumberOfBits={this.maxSeenLengthNumberOfBits}
                 showInfoColumn={showInfoColumn}
-                onBitFlipped={() => this.onBitFlipped()} />);
+                onValueChanged={() => this.onValueChanged()} />);
     }
 
-    onBitFlipped() {
+    onValueChanged() {
+        loglevel.debug("onValueChanged()");
         this.forceUpdate();
     }
 }
@@ -89,45 +91,58 @@ type ExpressionElementRowProps = {
     allowFlipBits: boolean,
     allowSignChange: boolean,
     expressionItem: ExpressionElement,
-    onBitFlipped: any,
+    onValueChanged: any,
     showInfoColumn: boolean
 }
 
 class ExpressionElementTableRow extends React.Component<ExpressionElementRowProps> {
     
     infoWasShown: boolean = false;
-    originalValue: Integer | null = null;
+    originalValue: Integer;
+    scalar: Operand;
 
     constructor(props: ExpressionElementRowProps) {
         super(props);
         this.state = { operand: null };
+        this.scalar = this.props.expressionItem.getUnderlyingOperand();
+        this.originalValue = this.scalar.value;
     }
 
     render() {
         const { sign, css, maxNumberOfBits, emphasizeBytes, allowFlipBits } = this.props;
         const scalar =  this.props.expressionItem.evaluate();
-        const bin = formatter.numberToString(scalar.value, 'bin').padStart(maxNumberOfBits, '0');
+        const padChar = scalar.value.value >= 0 ? '0' : '1';
+        const bin = formatter.numberToString(scalar.value, 'bin').padStart(maxNumberOfBits, padChar);
         const signBitIndex = scalar.value.signed && bin.length >= scalar.value.maxBitSize ? bin.length - scalar.value.maxBitSize : -1;
 
         return <tr className={"row-with-bits " + css}>
             <td className="sign">{sign}</td>
-            <td className="label">{this.getLabel()}</td>
+            <td className="label">
+                <span>{this.getLabel()}</span>
+            </td>
             <td className="bin">
                 <BinaryStringView
                     emphasizeBytes={emphasizeBytes}
                     binaryString={bin}
                     allowFlipBits={allowFlipBits}
                     signBitIndex={signBitIndex}
-                    onFlipBit={args => this.flipBit(args)} />
+                    onBitClicked={args => this.onBitClicked(args)} />
             </td>
             <td className="other">{this.getAlternative()}</td>
-            <td className="info accent1" data-test-name='ignore'>{this.props.showInfoColumn ? this.getInfo(maxNumberOfBits) : null}</td>
+            <td className="info accent1" data-test-name='ignore'>{this.props.showInfoColumn ? this.getInfo() : null}</td>
             <td className='undo' data-test-name='ignore'>
-                {this.originalValue != null ? <button title='Undo all changes' onClick={() => this.undo()}><FontAwesomeIcon icon={faUndo}/></button> : null}
+                {this.getUndoButton()}
             </td>
         </tr>;
     }
 
+    getUndoButton(): React.ReactNode {
+
+        return !this.originalValue.isTheSame(this.scalar.value) 
+            ? <button title='Undo all changes' className='undo' data-control="undo" onClick={() => this.undo()}><FontAwesomeIcon icon={faUndo}/></button> 
+            : null;
+    }
+
     getLabel(): string {
 
         // For expressions like |~2 
@@ -159,46 +174,43 @@ class ExpressionElementTableRow extends React.Component<ExpressionElementRowProp
     }
 
     undo() {
-        if(this.originalValue == null)
-            return;
-
-        this.props.expressionItem.getUnderlyingOperand().setValue(this.originalValue);
-        this.originalValue = null;
-        this.forceUpdate();
+        this.changeValue(this.originalValue);
+        this.props.onValueChanged();
     }
 
-    flipBit(args: FlipBitEventArg) {
+    onBitClicked(args: BitClickedEventArg) {
 
-        const op = this.props.expressionItem.getUnderlyingOperand();
         const { bitIndex: index, binaryStringLength: totalLength } = args;
 
-        const maxBitSize = op.value.maxBitSize;
-        const space = (totalLength - index - maxBitSize);
-        
-        if(this.originalValue == null)
-            this.originalValue = op.value;
+        const maxBitSize = this.scalar.value.maxBitSize;
 
-        if(totalLength > op.value.maxBitSize && space > 0) {
-            op.setValue(calc.addSpace(op.value, space));
+        if(!args.isTypeExtend)
+        {
+            const pad = this.scalar.value.maxBitSize - totalLength;
+            const newValue = calc.flipBit(this.scalar.value, pad + index);
+            this.changeValue(newValue);
+            return;
         }
-
-        const pad = op.value.maxBitSize - totalLength;
-        const newValue = calc.flipBit(op.value, pad + index);
-        op.setValue(newValue);
-        this.props.onBitFlipped();
-
-
+        
+        const space = (totalLength - index - maxBitSize);
+        this.changeValue(calc.addSpace(this.scalar.value, space));
     }
 
     onChangeSign () {
+        
         var op = this.props.expressionItem.getUnderlyingOperand();
-        if(this.originalValue == null)
-            this.originalValue = op.value;
-        op.setValue(op.value.signed ? op.value.toUnsigned() : op.value.toSigned());
+        
+        this.changeValue(op.value.signed ? op.value.toUnsigned() : op.value.toSigned());
+    
         this.forceUpdate();
     }
 
-    getInfo(maxNumberOfBits:number) {
+    changeValue(newValue: Integer) {
+        this.scalar.setValue(newValue);
+        this.props.onValueChanged();
+    } 
+
+    getInfo() {
         
         const op = this.props.expressionItem.getUnderlyingOperand();
         const { allowSignChange } = this.props;
diff --git a/src/expression/components/BitwiseResultViewModel.ts b/src/expression/components/BitwiseResultViewModel.ts
index 5569e26..76e55ff 100644
--- a/src/expression/components/BitwiseResultViewModel.ts
+++ b/src/expression/components/BitwiseResultViewModel.ts
@@ -2,6 +2,7 @@ import { Operand, ListOfNumbers, BitwiseOperation, Operator } from '../expressio
 import { ExpressionElement, Expression } from '../expression-interfaces';
 import calc from '../../core/calc';
 import formatter from '../../core/formatter';
+import exp from 'constants';
 
 type Config = {
     emphasizeBytes: boolean;
@@ -156,6 +157,8 @@ export default class BitwiseResultViewModel {
 
     static createModel(expr : Expression, emphasizeBytes: boolean) : BitwiseResultViewModel {
 
+        console.log(expr);
+
         if(expr instanceof ListOfNumbers) {
             return BitwiseResultViewModel.buildListOfNumbers(expr, { 
                 emphasizeBytes: emphasizeBytes, 
diff --git a/src/index.css b/src/index.css
index 0130e3e..46ddf1d 100644
--- a/src/index.css
+++ b/src/index.css
@@ -30,6 +30,8 @@ code { font-size: 1.2em; font-weight: bold; }
     background: rgba(0, 0, 0, 0);
 }
 
+.label { width: 5em; overflow: visible;}
+.label span {position: global;}
 .hidden { display: none;}
 
 .result { margin: 10px 10px 30px; }
@@ -71,7 +73,7 @@ a.hashLink { font-size: 1.1em;}
 
 .cur { color: lightgray; }
 
-.extra-bit { opacity: 0.4;}
+.extra-bit { opacity: 0.2;}
 
 button { border: none; text-decoration: underline;}
 
diff --git a/src/networking/components/IpAddressView.tsx b/src/networking/components/IpAddressView.tsx
index 71cd176..62c856f 100644
--- a/src/networking/components/IpAddressView.tsx
+++ b/src/networking/components/IpAddressView.tsx
@@ -34,7 +34,7 @@ export class IpAddressView extends React.Component<IpAddressViewProps>
             emphasizeBytes={false} 
             allowFlipBits={true}
             className={`octet-${octetNumber}`}
-            onFlipBit={e => this.onFlippedBit(e.newBinaryString, octetNumber, ip)} />;
+            onBitClicked={e => this.onFlippedBit(e.newBinaryString, octetNumber, ip)} />;
     }
     
     onFlippedBit(binaryString: string, number: OctetNumber, ip : IpAddress) {