Casio fx-115ES Plus

[Don Shepherd]

For a calculator that costs less than $20, this unit has some very interesting features, including:

1. Sigma and Product functions
2. Simplifies fractions
3. Simplifies square roots (normally found only on CAS calculators)
4. Finds prime factors (limited to factors up to 3 digits)
5. Equation solver
6. Reference last answer and the one before that!
7. Solves inequalities
8. Repeating decimals
   

The repeating decimals feature is particularly interesting. I entered a calculation that resulted in the fraction 385/1608. I pressed the key to get the decimal equivalent and it showed 0.239427860696517412935323383084577114 with a vinculum bar above the digits starting at 427. Amazing.