Re-scale of acceleration response history

[M. HAMZAH FANSURI]

Dear Colleagues,

I would like to ask how does re-scale of acceleration history? A given data of peak ground acceleration (a_max) is 0.21 g (Not provide acceleration history). I have found the acceleration history in PEER NGA but, I got a_max of about 0.19 g, it is provided acceleration history from PEER NGA.
Does anyone know how does re-scale the a_max from 0.19 to 0.21 g?
Thank you.