Precision and Accuracy

DISCLAIMER OF WARRANTY. The software is licensed "as-is." You bear the risk of using it. Gary Johnson gives no express warranties, guarantees or conditions. For practical purposes, do what engineers do, check and recheck your calcualtions using different methods and systems. This application uses the Javascript Eval function and floating-point arithmetic. Calculations done with this application will have floating point calculation errors.

For a more detailed understanding search for "what every scientist should know about floating-point arithmetic" or something like "precision and accuracy in Excel®".
The short story is humans are decimal and our world is infinite while computers are binary and most computer applications squeeze their numbers into a 32, 64 or 128 bit word.
Example: Numbers like 0.1, 1.3, and most other decimal fractions do not have exact representations as a binary floating-point numbers.

If we add 1 + 0.1 + 0.1 + 0.1 it equals 1.3.

Paste it into the Equation box and you will see something like 1.3000000000000003. which is extremely close to 1.3 but not exact. In practice, most of the time we just ignore the .0000000000000003 difference. I usually work to a precision and accuracy of 1/16 (0.0625) an inch or 1.905 centimeters. If hundredths of an inch / millimeters concern you, find another calculator.