Please help to minimize my code

Hi all!

I'm trying to make a "Scientific RPN Calculator" with an OLED display (128x32), an ATTINY85 and an one wire keyboard (with 16 keys) - and I'm almost done.

But now I ran out of memory (flash) - I'm at 7956 (of 8192) bytes.

My "dream" becomes true by implementing a "Key Typing Recorder" and "Statistic functions". Each of them would need approximal 400 bytes.

I spent many "days" to optimize the code, but now I have no more ideas.

So please help me to chase available bytes - every idea is highly appreciated.

See my code at GitHub - zooxo/scott: Scientific RPN Calculator with OLED display and ATTINY85.

Thanks in advance