HP 15c - Manual (Page 288)

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Chemical Substances
HP is committed to providing our customers with information about the
chemical substances in our products as needed to comply with legal
requirements such as REACH (Regulation EC No 1907/2006 of the
European Parliament and the Council). A chemical information report
for this product can be found at: www.hp.com/go/reach.
Perchlorate Material - special handling may apply
This calculator's Memory Backup battery may contain perchlorate and
may require special handling when recycled or disposed in
California.