Pre-AOS TIs--And they say RPN is complicated!?

[Gene]

Eh, the non-parentheses TI hierarchy followed MDAS (Multiplication/Division before addition and subtraction). It did this by a "sum of the products ability using a Z register to store the previous result (see the SR-51A owners manual online). It also used hierarchy that evaluated functions (trig, square root) as they were pressed.

It really wasn't THAT hard to use or understand, IMO. I used an SR-51A for years and found it very helpful.

My 2 cents.