Review miningInstall estimate
An install range derived from rating growth. Read as a band, never as an exact number.
Apple does not give install counts to third parties. The only thing measurable is the daily increase in ratings, and because the rate at which people rate is relatively stable, that increase moves in proportion to install volume.
It is an estimate, and presenting it as a single number would be misleading. rankcusp shows it as a band and says which observations it came from; where the measurement is insufficient it shows nothing rather than zero.