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Now try the same with a 5x8 character line LCD. 1st: Forget soft keys :( 2nd: You cannot display "RPN" or "ALG" or "RAD" etc. in a simple way the user can differentiate them as indicators :( Or is there a way I don't see?
True, you cannot display a string with narrower letters that would require use of the non-existent pixels in the space separating tne 5x8 blocks; but you can make any combination of pixels within a 5x8 block, so for example making the angle sign you have right in the middle of the display in your picture is not a problem. You can have up to eight different custom character definitions at a time, as if they were ASCII 00-07, although of course it would not true ASCII. You can re-define them on the fly.
In a project I worked on years ago, I had 32 custom characters, but we never needed more than a few at a time, so it fit well within the limit of eight. 28 of the customs were two characters in one block and two of them were actually three, stacked: "VOR" and "TWR". (The "R" had to be "r" since that can be displayed in a 2x2-pixel space.) As you've probably guessed by now, it was for an aircraft application. Any of your custom characters can appear as many times in the display as you want, as long as there are not more than eight cutom definitions at once.
Some of the characters often used in math are already included in the standard character set, so they would not have to be custom-defined. The LCDs I've worked with all had the alpha, beta, sigma (both upper-and lower-case), ro, square-root symbol, degree symbol, "-1" and "x" raised as exponents, theta, infinity symbol, capital omega, lower-case mu, X-bar, divide symbol, pi, left and right arrows, and the raised logical-AND dot built in, plus a bunch of Japanese characters I have no use for.
Graphics would be pretty limited. Horizontal bar graphs work out well though. Since there's a pixel row missing between 5x8 blocks, what I've done is to only use columns 1, 3, and 5 in each block, so it looks like a string of vertical marks with space between them, instead of being solid black for the whole length of the bar. A 40-character line then gives 121 possible lengths (including length 0) for bars in a bar graph. More than one bar per line is possible too.
As for soft keys, there's nothing that says the labels have to be displayed in inverse video.
