Computer keyboards have keys for some mathematical operators, but the multiplication sign isn't one of them. For this reason, programs that multiply numbers use the asterisk symbol to denote multiplication. The reason U.S. keyboards don't have a multiplication key is that they only represent the letters and symbols in the ASCII character set, so you must insert a special Unicode character to add a true multiplication sign to your document. Since the Unicode multiplication symbol looks almost the same as a lower-case "x," it's conventional to use this letter instead of a special character in some situations.
Using the Symbol Table
Most word processors have a special character table from which you can choose a Unicode symbol to insert at the cursor position. In Word, OpenOffice and LibreOffice, this table is located in the Insert menu. In Word, click "Insert" and choose "Symbol," and in OpenOffice or LibreOffice, click "Insert" and choose "Special Character." Since Unicode has thousands of characters, you can focus on a small subset by choosing a category from the Range or Subset menu, depending on your software. The multiplication symbol isn't part of Unicode's mathematical operators; it's in the Latin-1 subset.
Previewing and Inserting the Multiplication Symbol
You can preview the multiplication sign with various fonts by selecting a font from the Font Family menu in the special character table. The symbol's exact location in the Latin-1 subset is the hexadecimal value 0x00D7 or decimal value 0215. When you click a special character in the table, its hex and decimal values are displayed in the window, and since the Unicode characters are listed in ascending order, you can find the multiplication sign by clicking nearby symbols and searching forward or back as needed. When you find the multiplication sign, select it and click "Insert" to add it to the document.
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Using Keyboard Shortcuts
In Windows, you can use the Alt key codes to insert Unicode characters based on their decimal values. This technique works in text editors and word processors but not in all applications. To use this method, enable "Num Lock" and then hold down "Alt" while typing a character's decimal value on the number pad. On laptops, you must use the number pad keys 7, 8, 9, U, I, O, J, K, L and M, and on some laptops you must hold down "Fn" while typing. For the multiplication sign, type "0215" while holding down "Alt." When you let go of "Alt," the multiplication sign is inserted at the cursor position.
Multiplying Numbers on a Computer
To account for U.S. keyboards historically using ASCII encoding, computer software and programming languages almost always use the asterisk symbol for multiplication. Spreadsheets and software calculators that support entering symbols from the keyboard recognize the asterisk as the multiplication function. Some programs that source plain text configuration files recognize the lower-case "x" symbol as multiplication. For example, a video driver that stores your screen resolution in a text file may write it in human-readable format as "1680 x 1050."