The way this calculator works is that for any given raw score, the entire range of scaled scores that have shown up in the past are computed along with the percentage of times each one has shown up.
Your total score (out of 1600) will come from the math calculator and the reading and writing calculator (first two tabs). The separate reading calculator and the separate writing calculator at the end can be thought of as subscores that make up the full reading and writing score.
Note: Because of rounding, percentages may not add up to 100. We do not take into account curves from sections that had faulty questions.
Please bear in mind that this calculator is based only on the 10 past curves that have been released, which is not enough for a representative sample. Do not think that your scores are an error just because they are outside the range of scores this calculator gives you. It's impossible to know how The College Board has been changing up the SAT exam and setting the curves for the many exams it doesn't release. For example, the June 2018 exam had an extremely harsh curve because the exam was much easier than usual. We've treated it as an anomaly for now.