diff --git a/samples/calc-02/index.css b/samples/calc-02/index.css
index cf2038f..6993ee7 100644
--- a/samples/calc-02/index.css
+++ b/samples/calc-02/index.css
@@ -137,6 +137,10 @@ body {
 	justify-self: end;
 	font-size: 20px;
 }
+
+.stack-value.is-editing {
+	letter-spacing: 0.02em;
+}
 .display-buttons-panel {
 	padding: 8px;
 	min-height: 0;
@@ -379,6 +383,37 @@ button:active {
 	outline-offset: 2px;
 }
 
+.stack-value.is-editing {
+	display: inline-flex;
+	align-items: center;
+	justify-content: flex-end;
+	gap: 0;
+}
+
+.edit-text {
+	display: inline-block;
+	white-space: pre;
+}
+
+.edit-caret {
+	display: inline-block;
+	width: 1px;
+	height: 1em;
+	margin: 0 0.12ch;
+	background: currentColor;
+	animation: caret-blink 1s steps(1, end) infinite;
+	transform: translateY(0.02em);
+}
+
+@keyframes caret-blink {
+	0%, 49% {
+		opacity: 1;
+	}
+	50%, 100% {
+		opacity: 0.15;
+	}
+}
+
 .key-default {
 	background: linear-gradient(180deg, var(--btnTop), var(--btnBottom));
 	color: #eef2f7;
diff --git a/samples/calc-02/index.js b/samples/calc-02/index.js
index 06ae7ab..517fed7 100644
--- a/samples/calc-02/index.js
+++ b/samples/calc-02/index.js
@@ -94,6 +94,7 @@ function focusInput() {
 }
 
 let statusTimer = null;
+let editCursor = 0;
 
 function setStatus(message, isError = false, timeoutMs = 1400) {
 	if (!statusLine) return;
@@ -128,9 +129,14 @@ function getStackLine(indexFromTop) {
 	return indexFromTop >= 0 && indexFromTop < calc.stack.length ? calc.stack[indexFromTop] : '';
 }
 
+function getEditingDisplayValue() {
+	if (!calc.isEditing) return '';
+	return calc.inputValue;
+}
+
 function getStackDisplayValue(label) {
 	if (label === 'X') {
-		return calc.isEditing ? calc.inputValue : (calc.formatNumber(getStackLine(0)) || '');
+		return calc.isEditing ? getEditingDisplayValue() : (calc.formatNumber(getStackLine(0)) || '');
 	}
 	if (label === 'Y') {
 		return calc.isEditing ? (calc.formatNumber(getStackLine(0)) || '') : (calc.formatNumber(getStackLine(1)) || '');
@@ -157,14 +163,30 @@ function render() {
 	const isPortrait = window.matchMedia('(orientation: portrait)').matches || window.innerWidth <= 860;
 	calculatorEl?.classList.toggle('portrait', isPortrait);
 	calculatorEl?.classList.toggle('landscape', !isPortrait);
-	stackEls.X.textContent = getStackDisplayValue('X');
+	const xValue = getStackDisplayValue('X');
+	if (calc.isEditing) {
+		const cursor = Math.max(0, Math.min(editCursor, calc.inputValue.length));
+		stackEls.X.innerHTML = `<span class="edit-text">${calc.inputValue.slice(0, cursor)}</span><span class="edit-caret" aria-hidden="true"></span><span class="edit-text">${calc.inputValue.slice(cursor)}</span>`;
+	} else {
+		stackEls.X.textContent = xValue;
+	}
 	stackEls.Y.textContent = getStackDisplayValue('Y');
 	stackEls.Z.textContent = getStackDisplayValue('Z');
 	stackEls.T.textContent = getStackDisplayValue('T');
+	stackEls.X.classList.toggle('is-editing', calc.isEditing);
+	stackEls.X.classList.toggle('is-caret-visible', calc.isEditing);
 	updateCopyButtons();
 	modeButton.textContent = calc.angleMode;
 }
 
+function stopEditing(clearValue = false) {
+	if (clearValue) {
+		calc.inputValue = '';
+	}
+	calc.isEditing = false;
+	editCursor = 0;
+}
+
 function pushEditingValueIfNeeded() {
 	if (!calc.isEditing) return;
 	if (calc.inputValue !== '') {
@@ -172,20 +194,27 @@ function pushEditingValueIfNeeded() {
 	}
 	calc.inputValue = '';
 	calc.isEditing = false;
+	editCursor = 0;
 }
 
 function inputToX(value) {
 	if (!calc.isEditing) {
 		calc.isEditing = true;
 		calc.inputValue = '';
+		editCursor = 0;
 	}
 	if (value === 'Backspace') {
-		calc.inputValue = calc.inputValue.slice(0, -1);
+		if (editCursor > 0) {
+			calc.inputValue = `${calc.inputValue.slice(0, editCursor - 1)}${calc.inputValue.slice(editCursor)}`;
+			editCursor -= 1;
+		}
 	} else {
-		calc.inputValue += value;
+		calc.inputValue = `${calc.inputValue.slice(0, editCursor)}${value}${calc.inputValue.slice(editCursor)}`;
+		editCursor += value.length;
 	}
 	if (calc.inputValue === '') {
 		calc.isEditing = false;
+		editCursor = 0;
 	}
 }
 
@@ -217,11 +246,9 @@ function execute(name) {
 			}
 		} else if (name === 'clear') {
 			calc.clear();
-			calc.inputValue = '';
-			calc.isEditing = false;
+			stopEditing(true);
 		} else if (name === 'escape') {
-			calc.inputValue = '';
-			calc.isEditing = false;
+			stopEditing(true);
 		} else if (name === 'backspace') {
 			if (calc.isEditing) {
 				inputToX('Backspace');
@@ -235,7 +262,11 @@ function execute(name) {
 			}
 		} else if (name === 'neg') {
 			if (calc.isEditing) {
-				calc.inputValue = calc.inputValue.startsWith('-') ? calc.inputValue.slice(1) : `-${calc.inputValue}`;
+				const hasSign = calc.inputValue.startsWith('-');
+				calc.inputValue = hasSign ? calc.inputValue.slice(1) : `-${calc.inputValue}`;
+				if (!hasSign) editCursor += 1;
+				if (hasSign) editCursor = Math.max(0, editCursor - 1);
+				editCursor = Math.max(0, Math.min(editCursor, calc.inputValue.length));
 			} else {
 				calc.command('neg');
 			}
@@ -243,6 +274,9 @@ function execute(name) {
 			pushEditingValueIfNeeded();
 			calc.command(name);
 		}
+		if (!calc.isEditing) {
+			editCursor = 0;
+		}
 		render();
 	} catch (error) {
 		setStatus(error?.message || 'Operation error', true);
@@ -306,15 +340,34 @@ function handleKeyboard(event) {
 		'%': 'mod',
 		'^': 'pow',
 	};
-	const arrowMap = {
-		ArrowUp: upButton,
-		ArrowDown: downButton,
-		ArrowLeft: leftButton,
-		ArrowRight: rightButton,
-	};
-	if (arrowMap[key]) {
+	if (key === 'ArrowLeft') {
 		event.preventDefault();
-		arrowMap[key].click();
+		if (calc.isEditing) {
+			editCursor = Math.max(0, editCursor - 1);
+			render();
+			return;
+		}
+		leftButton.click();
+		return;
+	}
+	if (key === 'ArrowRight') {
+		event.preventDefault();
+		if (calc.isEditing) {
+			editCursor = Math.min(calc.inputValue.length, editCursor + 1);
+			render();
+			return;
+		}
+		rightButton.click();
+		return;
+	}
+	if (key === 'ArrowUp') {
+		event.preventDefault();
+		upButton.click();
+		return;
+	}
+	if (key === 'ArrowDown') {
+		event.preventDefault();
+		downButton.click();
 		return;
 	}
 	if (map[key]) {
@@ -459,7 +512,13 @@ constButton.addEventListener('click', (event) => {
 	toggleConstMenu();
 });
 
-leftButton.addEventListener('click', () => {});
+leftButton.addEventListener('click', () => {
+	if (calc.isEditing) {
+		editCursor = Math.max(0, editCursor - 1);
+		render();
+		focusInput();
+	}
+});
 downButton.addEventListener('click', () => {
 	if (!calc.isEditing && calc.isValidIndex(0)) {
 		const value = calc.stack[0];
@@ -472,6 +531,12 @@ downButton.addEventListener('click', () => {
 });
 
 rightButton.addEventListener('click', () => {
+	if (calc.isEditing) {
+		editCursor = Math.min(calc.inputValue.length, editCursor + 1);
+		render();
+		focusInput();
+		return;
+	}
 	execute('swap');
 });