def NRM(f,a,b,best):
    WARN = True    # Warn, rather than stop if I encounter a NaN...
    """ 
    Calculate NRM expected lab field and estimated ancient field
    NRM(blab,best)= (best/blab)*TRM(blab)
    """
    if float(f)==0:
        print('ERROR: NRM: f==0.')
    if not WARN : sys.exit()
    m = (old_div(float(best),float(f))) * TRM(f,a,b)
    return float(m)