this is my idea of the way to make the HP35s as a scientific calculator for general purpose and worldwide use.
Diferences with 4x series: (so they don't compete)
- no graphics.
- no I/O but a way to print with IR. no memory card, no saving or loading of programs.
- limited kind of value handled: numeric, complex, matrix, alpha, binary.
- no units attached to values.
- no RPL programming, mainly 41C RPN programming.
- short list of functions: the user manual is not a dictionnary of thousand of functions, quick/little learning.
keyboard usage: like on the HP41C
-short key press : execute the key.
-medium key press: display function name and execute.
-long key press: : display function name, display NULL and do nothing.
Keyboard labelling consistancy:
-unshifted function labelled on main part of the key.
-yellow shifted function over the top of the key.
-blue shifted function on sloped par of the key.
-alpha mode on bottom/right of the key (including space).
Keybord organisation: to respect as much as possible
-as many as possible usefull (in everyday usage) functions on unshifted keys.
-complementary or associated function is shifted on same key when possible
-programming functions on shifted key.
-Same as the Time module for the HP41C.
-Having a clock with multi-alarms is cool.
-Stopwatch permit to record fast laps (with a single key press) to registers and do analys after.
User mode: since it is general purpose, the user mode is a way to meet everyone's need (by assinging functions and programs to keys).
Letters on evrey key of first row:
-In a program, it permit to map local Lbl to keys
My fisrt keyboard layout: to be completed and improved
O is Over, F is Flat, S is sloped, A is alpha
O X^2 LN log XsqrtY L.R. E-
F sqrtX e^X 10^X Y^X 1/X E+
S ! nCr nPr S,o mX,mY ClE
A A B C D E F
O asin acos atan Pi R up %Chg
F sin cos tan i /\ %
S Alg RPN Rho Const Time/SW
A G H I J
O FN= Logic R down Matrix
F Sto Rcl = < \/ >
S Solve Intg Mode Flag Mem Display
A StoA RclA
O Alpha Xswap Abs () ClX
F Enter XswapY +/- EEX <-
S user Mod Rnd  Undo
A K L M N ClA
O Asn IP Cpx>X,Y D>Rad P>R
F XEQ 7 8 9 /
S Gto FP X,Y>Cpx Rad>D R>P
A O P Q R
O View Lbl
F Yellow 4 5 6 *
S Shift Pse Rtn
A S T U V
O Fix ISG X?Y H.MS-
F Blue 1 2 3 -
S Shift Eng DSE X?0 >H.MS
A W X Y Z
O off Sci /c prgm H.MS+
F on 0 . R/S +
S ./ Ab/C stop >HR
A space , ' "