Ten Key Calculator

What a ten key calculator is

A ten key calculator, often written 10-key, is an adding machine or desk calculator built around a block of ten digit keys. The 7-8-9 keys sit on top, 4-5-6 in the middle, 1-2-3 below and a wide 0 at the bottom, so every digit is within reach of one hand. That layout comes from the ten-key adding machine that Swedish-born inventor David Sundstrand filed for a patent in 1914, and it survives today as the numeric keypad on full-size computer keyboards. Telephones use the opposite layout, with 1-2-3 on top.

Older adding machines had a full column of keys for every digit position. The ten-key design let operators keep their eyes on the paperwork while their fingers entered numbers, and printing models recorded every entry on a paper tape. Accountants, bookkeepers, bank tellers and retail staff still use ten key calculators for long columns of figures.

How to use this ten key calculator

1. Type the amounts in the entries box, one per line, as you would key them into an adding machine. Type a minus sign in front of an amount to subtract it, for example −40 for a refund. A plus sign is optional. To multiply the running subtotal, type x 3 (or * 3); to divide it, type / 2.
2. Pick the decimal setting. F (floating) shows every digit. 2 is the usual setting for money, 0 shows whole numbers, and 4 suits unit prices and measurements.
3. Read the tape. The grand total appears at the top, with the item count and separate totals of what was added and subtracted. The tape table lists every entry with the running subtotal after it, just like a printed tape.

If an entry isn’t a number, the error gives its line number and text so you can fix that line. Don’t type thousands commas: the calculator asks you to type 1250 instead of 1,250.

Reading an adding machine tape

Here is a short tape at the 2-decimal setting, the kind a bookkeeper might run to check a day’s receipts and refunds:

The grand total is 202.04 from 5 items: 249.14 added and 47.10 subtracted. The item count is a useful check. If the tape shows 5 items but there are 6 receipts in the pile, one was skipped.

How bookkeepers use the tape

• Proving a deposit. Run every check on the tape and staple it to the deposit slip so the bank total can be matched to the individual items.
• Batch totals. Before entering a stack of invoices into accounting software, total them on a tape. After entry, the software’s batch total should match the tape exactly.
• Ticking and tying. Compare each tape line with its source document and tick it off. A wrong total can then be traced to the exact line instead of re-adding everything.
• Reconciling accounts. Starting with the statement balance, add deposits in transit and subtract outstanding checks. The tape’s final subtotal should equal the book balance.
• Extending a line item. Key the unit price, then x and the quantity, to check an invoice line: 18.75 then x 16 prints 300.00. A following / 2 splits it between two cost centers.

You can copy the result from this page or print it as a record. The arithmetic is exact, so a column of cents never picks up a stray 0.0000001 the way some spreadsheet sums do.

Ten key by touch: typing tips

Entering numbers without looking at the keys, called ten key by touch, is a skill employers test for accounting, payroll and data-entry jobs, usually measured in keystrokes per hour. The method is the same on a desk calculator and on a keyboard’s number pad.

• Home row is 4-5-6. Rest your index finger on 4, middle finger on 5 and ring finger on 6. The 5 key usually has a small raised bump so you can find home without looking.
• Each finger owns a column. The index finger types 1, 4 and 7, the middle finger 2, 5 and 8, and the ring finger 3, 6 and 9. The thumb presses 0, and the little finger reaches the + and Enter keys on the right.
• Return to home after every key. Reaching from home keeps your fingers oriented, which matters more than raw speed at first.
• Accuracy before speed. A fast operator who must re-run the tape loses more time than a slower, accurate one. Check the item count against your source before trusting a total.
• Practice with real columns. Short daily sessions entering receipts, invoice totals or practice sheets build speed faster than occasional long ones.

Using your keyboard’s number pad on this page

Turn on Num Lock so the number pad types digits instead of moving the cursor, then click in the entries box. Type an amount with the pad, press the pad’s Enter key to start a new line, and use the pad’s minus key for subtractions. The pad’s decimal key types the point. On a Mac keyboard, the number pad has a Clear key instead of Num Lock and types digits by default. Laptops without a number pad can use the number row, or a plug-in USB keypad.

The tape updates as you type, so you can keep your eyes on your source documents and glance at the subtotal column as you go.

Common mistakes

• Missing the minus. A refund or check keyed without a minus sign is added instead of subtracted, which throws the total off by twice the amount.
• Transposed digits. Typing 46.80 instead of 48.60 is a classic error. If a total is off by a number divisible by 9, a transposition is a likely cause.
• Wrong decimal setting. At the 0 setting, amounts with cents print rounded. Use 2 or F when cents matter.

To check a single decimal operation step by step, use the decimal calculator. To find the mean of a list of amounts, use the average calculator, and for tax on a total, the sales tax calculator.