991ES Plus (2nd Edition) help, please

[Steve Simpkin]

Yes the fx-115 and fx-991 model numbers have been used for many different Casio calculators over the years. One reason they probably keep reusing them is because the numbers are approved on a number of standardized tests. For example the Fundamentals of Engineering (FE) exam, offered by the National Council of Examiners for Engineering and Surveying (NCEES) approves only a small number of Casio, HP and TI calculator models for the exam.

“The NCEES approves all fx-115 and fx-991 models for use on its exams. Their policy states that “any Casio calculator must have ‘fx-115 ‘ or ‘fx-991’ in its model name.””

Sadly the two approved HP models (HP 33s and HP 35s) are no longer in production.

https://fundamentalsofengineering.com/fe...ators.html