Two PHP questions

First of all, what exactly is get/set_magic_quotes_runtime? (I know what a get/set function does, and I know what magic_quotes does, but I'm unclear about what magic_quotes_runtime is as opposed to _gpc). Does it get the magic_quotes setting at runtime, before anything has been set_magic_quotes_runtime'd? I sort of get that it has to do with returning slashes with quotes in a function as opposed to doing it when a function is called. Any clarifications? The only comment on the PHP list says that it's being turned off, so I guess it's not that important. Secondly, is there any way of counting how long in pixels my page runs? Basically, my situation is this: I want to know if my page runs more than a screen and a half (or so... still deciding) of the user's screen so that I can put a Go to Top link on the bottom if it's useful. Any ideas? Thanks in advance!