the next step would be replace 4M oscillator
my stable with 12 ( if i remember right) , caps measure you need to divide
and beeper sound too thin ... ; but it really fast now
i have another one it works with 24M ( was 4M), super fast, i use it to probe resistors .... an auto range count down in a blink ...
upd: TO-92 are Vref, next to are small cap shunt, that not enough, so 1-10uf tant. would be much better ....