---
title: The built-in calculator (F1)
order: 7
updated: 2026-07-21
---

# The built-in calculator (F1)

Press **F1** anywhere in the app and a calculator opens over whatever you were doing. Press **Esc**, or click outside it, to close it again — nothing you had typed on the screen behind is lost.

It is not a copy of the calculator that ships with your computer. That one can add and multiply; it cannot tell you what discount gets a customer to ₹28 a piece, what a price looks like once GST is stripped out of it, or what a 40 mm round bar 6 metres long weighs in mild steel. This one is built around the arithmetic that actually comes up while quoting, purchasing, and billing.

The calculator is arranged as a column of sections down the left side. Click a section to switch to it; the section you were last on stays selected while the calculator is open.

Most sections start with a **What do you want to find?** dropdown. Pick the question you are trying to answer and the inputs change to suit it — you always type in what you know and read off what you don't.

**Every answer can be copied.** Click any result and it is copied to the clipboard, ready to paste into a rate field, an email, or a note. The value copied is the full-precision number, not the shortened version on screen.

Results appear as you type. There is no *Calculate* button, and nothing you do inside the calculator changes any record — it is a scratchpad, not a form.

## Basic

An ordinary calculator, plus a **tape**.

The keypad has the usual digits and operators, along with `%`, `√`, `x²`, `1/x`, sign flip (`±`), backspace (`⌫`), clear-entry (`CE`), clear-all (`C`), and the five memory keys (`MC`, `MR`, `M+`, `M−`, `MS`). Memory is shown under the keys whenever it holds something other than zero.

You can drive it from the keyboard instead of clicking:

| Key | Does |
|---|---|
| `0`–`9`, `.` | Enter a number |
| `+` `-` `*` `/` | Choose an operation |
| `Enter` or `=` | Get the result |
| `Backspace` | Delete the last digit |
| `Delete` | Clear the current entry |
| `%` | Percentage |
| `R` | Square root |

The keyboard only drives the keypad while the *Basic* section is on screen, and never while your cursor is inside an input box.

The **tape** on the right lists everything you have worked out this session, newest first — the sums as well as the answers. This is the part people come back for: after adding up fourteen line items, you can check what you actually keyed in rather than starting over. **Click any line in the tape to bring that result back into the display** and carry on calculating with it. *Clear* empties the tape.

`%` behaves the way a desk calculator does, not the way a spreadsheet does: `200 + 10 %` gives **220** (ten percent *of 200*, added on), while `200 × 10 %` gives **20**. Pressing `=` repeatedly repeats the last operation.

## Discount

The section for anything involving a percentage off a price.

- **Price after discount** — the straightforward one. Give a list price and a discount percentage; you get the discount amount and the net price. Add a quantity and it also totals the line.
- **Discount % needed for a target price** — the reverse, and the reason this section exists. The customer says *"do it at ₹28"*; enter the list price and ₹28 and you are told the percentage to write on the quotation. If the target is *above* the list price, the calculator says so plainly rather than showing a negative discount.
- **Price before discount** — you know the net rate and the discount that was applied, and you need the list price it came off.
- **Multiple discounts one after another** — for price lists that carry a chain like *10% + 5% + 2%*. Those do **not** add up to 17%; each one applies to what is left after the previous. The calculator gives the true **effective single discount** and, next to it, the straight sum so you can see how far off the quick mental answer is.
- **Selling price from cost + margin** — enter what the item costs you and the margin you want to keep, and get the price to quote, along with the equivalent markup on cost.
- **Margin & markup from cost + selling price** — enter cost and selling price and get the profit, the margin, and the markup.

Margin and markup are different numbers and the calculator always labels which is which: **margin** is profit as a share of the *selling price*, **markup** is profit as a share of the *cost*.

## GST

- **Add GST to an amount** — taxable value in, invoice total out.
- **Remove GST from an inclusive amount** — the common one. A supplier quotes *"₹11,800 all inclusive"*; this tells you the taxable value and the tax sitting inside it.
- **Find the GST rate from two amounts** — you have a before-tax and an after-tax figure and want to know what rate was applied.

For the first two you also choose the **supply type**, because that decides how the tax is split on the invoice:

- **Same state** — CGST and SGST, each at half the rate.
- **Other state** — IGST at the full rate.

The rate starts at **18%** — the rate on the large majority of invoices — and is typed over for anything else (0.25%, 3%, 5%, 12%, 28%, or a rate of your own).

## Units

Pick a **category** first, then the unit you are converting **from** and **to**. *Swap* flips the two.

Available categories: length, weight, area, volume, temperature, pressure, power, flow rate, speed, and time — including the units this trade actually uses, such as quintal and metric tonne, guntha and bigha, kg/cm² and mmWC, metric HP and BHP, TR, LPM and CFM.

Below the answer, the same value is listed in **every** unit of that category. When you are not sure which unit the other side wants, this saves a second conversion.

Temperature is handled properly as a scale conversion, so 0 °C reads as 32 °F rather than 0.

## Mensuration

Areas, volumes, and — the point of the section — **weight from dimensions**.

Choose a shape, choose the unit you want to type in — **millimetre, centimetre, metre, inch or foot** — and enter the dimensions. Millimetre is the default because that is how a drawing arrives, but a site measurement in feet or metres can be entered as-is instead of being converted by hand first.

Changing the unit re-reads the figures you already typed in the new unit, so entering `2` and switching from millimetre to centimetre gives you 2 cm — it does not convert 2 mm into centimetres. Everything downstream (areas, volumes, weights) is unaffected by the choice; only the numbers you type are interpreted differently.

Flat shapes (rectangle, circle, ring, triangle, trapezium) return an area in mm², cm², m², sq ft, and sq in, plus extras such as perimeter or circumference where they apply.

Solid shapes (plate/sheet, round bar, square bar, hex bar, flat bar, pipe, square/rectangular tube, cylinder, sphere, cone, box) return a volume **and** a weight. For those, also pick a **material** — mild steel, SS 304/316/202, cast iron, aluminium, brass, copper, bronze, lead, zinc, nylon, PVC, HDPE, acrylic, teak, rubber, glass, or water — or type a **custom density** in g/cc, which overrides the material.

Enter a **quantity** and everything is totalled for that many pieces, with the per-piece weight still shown alongside.

Extra readouts such as a circumference or a pipe bore come back in whichever unit you are typing in, so they can be measured against the same tape.

Hollow sections need a wall thinner than half the outer size, and every dimension must be greater than zero; until that is true the calculator says what is missing instead of showing a wrong number.

## Finance

The money-over-time questions around payment terms.

- **Payment due date from credit days** — invoice date plus a credit period gives the due date and how many days remain, or how many days it is overdue.
- **Days between two dates** — also expressed in weeks, months, and years.
- **Interest on an outstanding amount** — simple interest on a principal at a yearly rate, over a duration you give in days, months, or years. It also breaks the rate down to interest per day and per month, which is what usually goes on a debit note.
- **TDS deduction** — pick the common section rate (194C at 1% or 2%, 194H / 194-I at 5%, 194J at 10%, 194Q at 0.1%) or type your own, and see the deduction and the net payable to the party.
- **EMI on a loan** — monthly instalment, total interest, and total repayment.

Interest here is **simple interest**, not compound. That is deliberate — it matches what a firm can reasonably charge a customer for a late payment.

## Number

The small conversions that surround paperwork rather than pricing.

- **Amount in words** — the Indian format used on cheques and invoices, complete with lakh and crore, paise, and the closing *Only*.
- **Lakh / crore against million / billion** — the same figure shown on both scales, for when a foreign supplier or customer is on the other end.
- **Percentage increase or decrease** — between an old and a new value, with the difference alongside.
- **Round off to the nearest figure** — to paise, 0.05, 0.50, a rupee, 5, 10, 100, or 1,000, showing the rounded value, the round-up, the round-down, and the round-off difference.
- **What percent is one number of another** — a share, plus what is left over.

## Common questions

### Does the calculator change anything in my records?

No. Nothing typed into it is saved and nothing is sent to the server. Copy a result and paste it where you need it.

### Are the answers exact?

Yes to every digit you will ever act on. Results are worked out at full precision and only rounded when they are drawn, and clicking a result copies the **unrounded** number, not the shortened one on screen. Chained working keeps its precision too — `1 ÷ 3 × 3` comes back to `1`, not `0.999999999999`.

### Why did my figures disappear when I switched sections?

Each section clears when you leave it, so you always come back to a clean set of inputs. The one exception is *Basic* — its display, memory, and tape survive a trip to another section and back, for as long as the calculator stays open.

### Can I open it while another window is already open?

Yes. F1 works on top of an open record, an open form, or another pop-up window, and closing the calculator returns you to exactly what was underneath.

### F1 opened my browser's help instead

That should not happen inside the app — the app claims the key first. If it does, click once anywhere on the app's page so it has keyboard focus, then press F1 again.