The trend in commoly available cheap scientific calculators is that when you want to calculate a function like sin( sqrt(2)/5) , the most convenient thing to do is press the sin() key first. Twenty years ago (or less) when using the "algebraic" calculator interface (on some fairly expensive calculators), the most convenient thing to do was to work out sqrt(2)/5 first and then press the sin() key. That style interface was useful if you did rough estimates of the work as you progressed. You could mentally check if sqrt(2) looked correct, then check if dividing by 5 looked correct and if you were good at trig you might see if the sin() looked right. If you weren't good at trig you could trust your manual dexterity to press the sin() key instead of something else. I think the modern trend is to check the visual appearance of the formula on the display. So you check if the display is showing a formula that is correct instead of checking that the stages in the calculation make sense numerically. People who do computer programming or even just spreadsheet programming develop skill at checking the visual appearance of formulas. Perhaps better displays and more people who can check formulas explains the modern trend in calculator interfaces. I'm curious whether any of the expensive Texas Instrument calculators have an option to change the interface to the old fashioned style - if they no longer use that style as the default.