There is no such thing in the rules of chess as a draw by perpetual check.
Resolved: Draw by repetition and perpetual check
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Okay, lets get a few things straight:
1. There is no draw by perpetual check, it is either a draw by way of repetition or the fifty move rule.
2. Draws by repetition and the fifty move rule must be claimed, as per FIDE rules.
3. Sites that automatically award these draws, have made their own rules up.
4. Draws fulfilling the relevant criteria, may be claimed by hitting the draw button, at the proper juncture.
5. The answer to this and similar questions have been dealt with many times and may be found with a simple search. Enter likely keywords in the little window, top-right of this page (next to "Search"), then hit enter.
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