standard temperature

hi

why in this video the standard temperature is rated at 20 degC instead of 15 ? and the comp table shown start at 0 degC instead of the standard temp , i assume the 0 is for the std temp and we should build the table from there (so 0 mean 15 , 10 mean 25 ... etc) , from my experience ...... -12.5% at 50deg celcius catched my attention , i just need more details or maybe i miss something lol

thanks

iat comp video