Rating based on 2 criterias

Question

I'm trying to write rating system which scores items based on two criteria with different importance. Criteria_1 will have importance 0.2 and Criteria_2 will have 0.8. Maybe a bit of trickiness adds the fact that Criteria_1 will have values of few thousands and Criteria_2 will have values of less than 1000 most of time and that gives me a bit of doubt about decision of trying to create rating based on criteria with such a big difference in values being wise. Nevertheless, I'd like to create system based on both, therefore I'd be glad if you provided me with some formula (if there is any) which would consider both criteria and their importance and produce some kind of numerical score.

Answer 1

As a rough guide:
1) Estimate the spread of Criterion_1 (if this is usually between 500 and 1100, then Spread_1=1100-500=600.)
2) Estimate the spread of Criterion_2, call it Spread_2

During the program, calculate 0.2*(Criterion_1/Spread_1) + 0.8*(Criterion_2/Spread_2)

There are ways to calculate the spread, called the 'standard deviation,' if you want a better rule.