ADS is almost universally used as a research tool among astronomers, and there are several studies that have estimated quantitatively how much more efficient ADS has made astronomy; one estimated that ADS increased the efficiency of astronomical research by 333 full-time equivalent research years per year, and another found that in 2002 its effect was equivalent to 736 full-time researchers, or all the astronomical research done in France. ADS has allowed literature searches that would previously have taken days or weeks to carry out to be completed in seconds, and it is estimated that ADS has increased the readership and use of the astronomical literature by a factor of about three since its inception.