Why Hewlett-Packard calculators in a Texas Instruments collection???
Because I couldn't resist the first two HP programmable calculators that aren't in RPN mode but use direct algebraic notation.
The HP 20S and the HP 21S must have, at the time of their release, angered Hewlett-Packard aficionados who were fervent followers of reverse Polish notation.< BR> As for the HP 35S, it can be used indifferently in "Polonaise" or "Algebraic".
Then, the HP 30S with its "programming" by formulas made me think of the TI-60X, TI-68...
Those "algebraic" Hewlett-Packard programmable calculators were worth looking into
... then some RPN Hewlett-Packard calculators also curiously attracted me...

I had long been interested in the ET-57 and ET-58 of Miroslav Nemecek, clones of TI unfortunately not sold.
But my curiosity about Hewlett-Packard calculators made me discover some very interesting clones:

the WP-34S obtained by "flashing" the firmware on an existing calculator is a little gem (with USB and InfraRed) but the keyboard is a little loaded or even too dense...

the PX15C, PX16C and PX41C by Alex Garza have really seduced me by their simplistic appearance but their power and finish. Very nice work.

as for the DM42 from SwissMicros...nothing to say...I take it everywhere with me! (I would be tempted by the DM41X...)