When using theoretical calculations, it is often a good idea to express calculations and data in significant digits. A calculation has the same number of significant digits as the number in the original problem with the least amount of significant digits. Here are a few rules for significant digits.

- All nonzero digits are significant.
- All zero digits which are the final digit after the decimal point are significant.
- All digits in between significant digits are significant.
- All other digits are not significant.

You may have to use scientific notation to express some significant digit calculations, such as 49+51, which equals 100, but since "100" has one significant digit, you must express it as (1.0 * 10^2) or 1.0E2. Some practice:

- 321: 3
- 300: 1
- 0.000003: 1
- 0.300000: 6
- 3.205: 4
- 7.0000000000000000000: 20