How to turn ATTiny PB5 RESET and I/O pin into a regular I/O PIN? Changing RSTDIS

I've noticed the opposite. I've tuned a couple and despite similar conditions (V and T) the two required relatively different OSCAL values.

yes, i also noticed factory oscal values vary considerably from chip to chip. and after tuning ended up with correspondingly different settings. but in my tests the actual deviation from stock quite small. since about 15yrs ago, when they first became available, ive been tracking m8 offsets. initially they were all over the place. as years passed apparently atmel tightened production specs. the a version and modern tinies etc seem even better. iirc they even guarrantee less than 1% on some which is more than enough for serial. so for hobby use i routinely skip tuning and even consider doing so for non-critical commercial projects. for example in spite of 10% spe, looks to me like typical max deviation (2%) is not as bad as the divisor error using a crystal (4%).

of course this all depends on the application and individual risk assement. certainly not adequate for rtcc.

If it were an application where the reset pin wasn't disabled, or a DIP package were used, I probably wouldn't bother tuning as its easy to unbrick the chip if the bootloader fails. But if the bootloader is the only way left of programming the chip without HV programmers, then I would be much more cautious.

you know what cracks me up? one fellow on freaks has as his avatar signature "no rstdsbl, no fun". lol! i bust a gut every time i see that.