1. Do the divisions on a scale always have to be equal?
No, it is possible to have a non-uniform scale.
Examples of non-uniform scales are the scale that measures earthquakes (the Richter scale) and scales on radio dials.
e.g. On the Richter scale of earthquakes which goes from 1 to 8. An earthquake of magnitude 8, which is a great earthquake is not twice as severe as an earthquake of magnitude 4 (slight damage within a small area). It is much more serious.
2. Why is it so important to put the units next to values in tables?
Although it is sometimes obvious what the units are, there can be confusion. e.g. Is the time am or pm?
Is the dollar value in US dollars or NZ dollars?
Is the temperature in degrees centigrade or degrees farenheit?
Many countries use metric units but some still use older systems.