That's okay! We don't really need the exact date.
We ask this question because if it was calibrated or purchased recently (within the last 6 months), then we won't send out the calibration service reminder for it until it's due. (We recommend calibration every 6 months from the date of purchase.)
So if it was NOT purchased or calibrated within the last 6 months, then we'll e-mail the service reminder to you right after your plan is set up.