The helpfile for simple check's has a typo.

Steps to take: 1) add a new item, 2) set type to "simple check" and 3) click on the question mark for the "key". The page "popup.php?dstfrm=web.items.item.php&dstfld1=key&srctbl=help_items&srcfld1=key_&itemtype=3" will be loaded. The entry for "tcp,port" says "[...] the serivce on the port is down [...]". Obviously, this should read "service".