The parameter of Peak function

Please tell me about "change" parameter in Peak function. i checked https://www.amibroker.com/guide/afl/peak.html but it don't talk about it. Thank you!

The Users Guide talks about it, quote:

Peak [...] - this function is based on Zig-Zag indicator and may look into the future.

Then http://www.amibroker.com/guide/afl/zig.html

If you don't know what zig zag indicator is you can find it out easily: https://www.google.com/search?q=zig+zag+indicator