import pandas as pd
from datetime import datetime
def calibration_check():
instruments = pd.read_sql("SELECT * FROM instruments")
now = datetime.now()
for _, inst in instruments.iterrows():
due = pd.read_sql("SELECT due_date FROM calibration_records WHERE instrument_id = ?", inst['id'])
if not due.empty:
days_left = (due['due_date'] - now).days
inst['status'] = 'Overdue' if days_left < 0 else 'Due Soon' if days_left < 30 else 'Compliant'
return instruments