This has to do with the stylesheet used to display content within PageTurner. It defaults to “root” so it can be left out of the URL for any given page.
This is the zoom level (percent). The pageturner supports 50, 75, 100, 125, 150, 175, 200, 300, 400.
This is the sequence number the image has in the digitized file. The sequence starts at the cover page and goes sequentially all the way through the volume. The sequence number value is subject to change (for instance, if a page were missing in the original image sequence and inserted later), but the sequence number itself is present for every image in the repository, as is the volume id. Thus, the two values required to access a given page are the volume id and the sequence number.
By contrast, the num parameter is the scanning source’s (Google, IA, local, etc.) attempt to represent a volume’s page number. This is not always present, or may there may be multiple page numbers within a volume (e.g., volumes that are bound together).
Es genügt also, wenn man ID und seq angibt: