Always trust your calculators

The reason behind this calculation is that in most Chinese ROMs, the % operator is not interpreted as a percentage of the last number (for example, 10% of 100), but as n/100. This means that calc in CN ROMs calculates as 100-(10/100) = 100 - 0.1 = 99.9

Basically, it's mostly a difference between Casio-style and TI-Style.
20% in Casio style is 20 percent of the preceding number (literal) while in TI, percentage is divided by 100. So, the calculator in CN ROMs treated percentage as pure unary operator.

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