Here is the manual link
Press CTRL+F Type in 'tax' top right, press Enter. Scroll through the 19 mentions, Number 3 shows it. Copied and pasted below, but it doesn't show symbol image. The first paragraph covers getting into setting mode and setting date and time, then comes 'Tax Rate'.
https://www.manuallib.com/download//SHARP-EL-1801PIII-OPERATION-MANUAL.PDF
GT • RATE SET GRAND TOTAL / RATE SETTING MODE SELECTOR: "GT": Grand Total "•": Neutral "RATE SET": To set the date, time, and tax rate, set this switch at the "RATE SET" position. Date: • Enter in the order of month, day and year, then press to complete the entry. • Use to separate month, day, and year. • When is pressed, the number entered is evaluated and displayed as "date" if the value is within the following range; "Error" is displayed otherwise, and the previously set date is restored. Month: 1 - 12; day: 1 - 31; Year: 2000 - 2099 (in 4 digits) or 00 - 99 (in 2 digits) Time: • Enter in the order of hour, minutes, then press to complete the entry. (There is no entry available for the seconds value. The clock starts at zero second.) • If the hour/minute digit is less than 10, it is not necessary to enter the first digit "0". • Use to separate hour and minute values. • When is pressed, the number entered is evaluated and displayed as "time" if the value is within the following range; "Error" is displayed otherwise, and the previously set time is restored. Hour: 0 - 23 (24-hour system for the hour entry), Minute: 0 - 59
Tax rate: • Press three times, enter the tax rate, followed by . • A maximum of 4 digits can be stored (decimal point is not counted as a digit). • Only one rate can be stored. If you enter a new rate, the previous rate will be cleared.
more here and videos
https://www.google.com/search?q=sharp+el-1801piii+set+tax+rate
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