Change Sign Key on Calculator: Where It Is & How to Use It

To change the sign of a number on a standard calculator, press the key labeled (−), +/-, or CHS (change sign) after entering the number. This key toggles the displayed value between positive and negative without needing to subtract from zero. The exact label and location vary by calculator model, but the function is universal across basic, scientific, and financial calculators.

Formula

The change-sign operation is not a formula but a unary operation: it multiplies the current displayed number by −1. In algebraic notation, if the displayed value is x, pressing the key produces −x. On RPN (Reverse Polish Notation) calculators, the key is often labeled CHS and operates on the number in the display or the top of the stack. There is no hidden arithmetic; the key simply flips the sign bit of the stored number.

Worked Example

Suppose you want to enter −25 on a basic calculator. With the default display showing 0:

1. Press 2, 5 → display shows 25.
2. Press +/− (or (−)) → display shows −25.

If you press the key again, it returns to 25. On a scientific calculator, the key is usually near the bottom row, often labeled (−) to distinguish it from the subtraction operator −. On an RPN calculator like the HP 12C, you enter 25 then press CHS to get −25. The result is always the same: the sign of the displayed number flips.

Where to Find the Key on Different Calculator Types

• Basic four-function calculators: Look for a small key labeled +/− or CHS, usually on the left side or near the equals key. Some models place it above the digit keys.
• Scientific calculators (Casio, Texas Instruments): The key is typically labeled (−) and located near the bottom, often just above the 0 or to the left of the . (decimal) key. It is not the same as the subtraction key.
• Graphing calculators: The negative sign is usually a separate key, often labeled (−) or (-), distinct from the minus operator. On TI-84 Plus, it is the key with (−) above the 3.
• Financial calculators (HP 12C): The key is labeled CHS and is located in the left column, near the ENTER key.
• Smartphone calculator apps: In portrait mode, you may need to rotate to landscape to see the +/− key. In some apps, it appears as a small toggle near the display.

Common Mistakes and Misconceptions

A frequent error is using the subtraction key − instead of the change-sign key. On most calculators, pressing − then a number does not make that number negative; it starts a subtraction operation. For example, entering − 5 on a basic calculator often results in an error or a pending operation, not −5. Another misconception is that you must enter the sign before the number; in fact, the change-sign key works after the number is displayed. On some calculators, you can press it before typing a number, but the standard order is number first, then sign toggle.

When You Actually Need the Change-Sign Key

The key is essential for entering negative numbers in any calculation, but it becomes particularly important in:

• Scientific notation: Entering a negative exponent, such as 1.5 × 10â�»Â³, requires pressing +/− after typing the exponent.
• Negative temperatures: Inputting −10°C for a conversion or calculation.
• Financial calculations: Representing cash outflows (negative cash flows) in TVM (time value of money) problems on financial calculators.
• Programming and graphing: Defining negative coefficients or coordinates.
• RPN calculations: The CHS key is used constantly in stack-based arithmetic to change the sign of a number before an operation.

How to Choose the Right Key for Your Calculator

If you are unsure which key changes the sign, look for a label that includes a minus sign but is not the standard subtraction operator. Common labels are +/−, (−), CHS, or NEG. On calculators with a separate negative key, it is usually placed near the decimal point or the bottom row, away from the arithmetic operators. If you have a manual, check the index for “negative� or “change sign.� On a computer’s on-screen calculator, the key is often labeled F or ± depending on the operating system. When in doubt, test it: type a number, press the key, and see if the sign flips.

Limitations and Edge Cases

The change-sign key operates on the number currently in the display, so it cannot change the sign of a number that is part of a pending operation unless you first complete or clear that operation. On some calculators, pressing +/− during an operation may affect the next number entered rather than the displayed one. Also, the key does not work on special values like infinity or NaN (not a number) on graphing calculators. For very large or very small numbers in scientific notation, the key flips the sign of the mantissa, not the exponent, which is usually what you want. If you need to change the sign of an exponent, you must press the key while the exponent is being entered, not after the full number is displayed.

Frequently Asked Questions

Why does my calculator have both a minus key and a negative key?

The minus key (−) is a binary operator: it subtracts two numbers. The negative key (+/− or (−)) is a unary operator: it changes the sign of a single number. They serve different purposes, and using the wrong one leads to errors, especially in scientific calculations where a negative number is an operand, not an operation.

Can I change the sign of a number after I press equals?

No. Once you press equals, the result is computed and the change-sign key will flip the sign of that result, not the original input. If you want to change the sign of an input, do it before pressing equals.

How do I enter a negative number on a phone calculator?

On most phone calculator apps, rotate the phone to landscape mode to reveal the +/− key. In some apps, it is already visible in portrait mode. If not, look for a key with a plus and minus sign combined. Enter the number first, then tap that key.

Is the change-sign key the same as the subtract key on a graphing calculator?

No. On graphing calculators like the TI-84, the (−) key is a separate key, usually located to the left of the ENTER key or above the 3. The subtraction key is the blue − on the right side. Using the wrong one will produce a syntax error or an unintended operation.

What does CHS stand for on an HP calculator?

CHS stands for “change sign.� It is used on RPN calculators to negate the number in the display or the top of the stack. For example, to enter −42, you type 4, 2, then press CHS.

Can I change the sign of a number in the middle of a calculation?

Yes, but only if the number is currently displayed. For instance, if you are computing 5 × −3, you would enter 5, press ×, then enter 3, press +/−, and then press equals. The key flips the sign of the 3 before the multiplication is executed.

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