Approval voting requires only addition. The candidate with the most votes wins, and results from multi-candidate elections are easily shown in bar graph form.

RCV, however, uses a more complicated algorithm:

Total all the first-choice votes. If a candidate has greater than half these votes among the valid ballots, then elect that candidate. If not, then eliminate the candidate with the least first-choice votes. Look at the ballots from that eliminated candidate. Transfer that candidate’ next-choice votes to those candidates and treat those votes as first-choice votes. Again, look to see if a candidate has greater than half these first-choice votes among the remaining valid ballots. If there is again no winner, then repeat this process until a candidate has greater than half the total votes among the remaining valid ballots.

For an example of how this calculation process looks in practice, see an example from a real Oakland, CA mayoral RCV election. Note that this is a simplified version in that it omits the first five rounds.