How is the overall "star" rating compiled? Is it simply an average of every rating?
I think a hybrid system using Amazon's "Was this review helpful" to add weight to each review. If it's obviously a garbage review, people would vote down the individual review, thus giving lower weight to how it effects the overall average.
Reading some of those reviews, it doesn't appear that people are complaining about the number of conversions, rather they don't understand why you included unit conversions that don't make sense in the context your app claims to target. Which actually seems like a legitimate criticism, IMO.
Not to mention that units get merrily mixed up. Quoting one review, "For example, if you have 1 honey, that's 1.44 grams per cubic centimeter, but if you have 10 honey, that's 14.4 grams per cubic centimeter (more dense than lead)." Err, wut?
But at least I learned that there are 2000 egg yolks in 80 PSI.