[. . . ] CITIZEN model CT-500 is a dual-powered (high power solar + back-up battery) calculator operative under any lighting conditions. [. . . ] eRROR Before performing each calculation , press [ON/C] & [ RECALL ] keys. Input each calculation twice to compare, press [ ] key to call out the Difference, use [ PRE/NOW ] key to review to and fro the previous input and now input until all mis-inputs are corrected. A single calculation is invalid to compare / correct; calculations more than two expressions, only the last two are compared. En If you want to dispose this product, do not mix with general household waste. There is a separate collection systems for used electronics products in accordance with legislation under the WEEE Directive (Directive 2002/96/EC) and is effective only within European Union. The symbol in this information sheet means that used batteries should not be mixed with general household waste. [. . . ] If you wish to discard used batteries, please contact your local authorities or dealer and ask for the correct method of disposal. [. . . ]