Figure 1.14 uses size comparisons in the universe to introduce scientific notation. This dynamite site, called “Powers of Ten” is not to be missed. Do not be impatient as it loads — it is worth the wait.
Scientific Notation in Everyday Life, Significant Digits:
We introduced calculators in this section, and even though I try not to recommend commercial sites, I will make these two an exception. Both Texas Instruments and Hewlett Packard have excellent sites, with a great deal of useful information: