Visiolink's server logs count the number of pages that are being downloaded (within a given time period). These pages are split between the number of publications. The number of downloads from the server log is, therefore, an expression of entire downloaded publications. The process is the same for pages downloaded on e-pages and devices.
The Download Event in Google Analytics counts a download as soon as a reader opens a publication via the Coverflow for the first time - even if not all of the publication's pages are downloaded.
The two different counts of downloads cause a natural discrepancy between downloads from Visiolink's server logs and the Download Event in Google Analytics. Both figures are correct but they are based on different counting methods.
If a publication of 50 pages is opened and page 1 is read by 50 people, Visiolink's server log will count this as 1 download. In Google Analytics the Download Event will track 50 downloads since the publication has been opened 50 times.
If one person reads 50 pages in a publication of 50 pages the Visiolink server logs count 1 download. Google Analytics will also only track 1 download since the publication only has been opened once.