def p_test_loc_uty(α_spt, p_lt, p_li, p_e):
    """Local test pressure unity check.

    Reference:
    DNVGL-ST-F101 (2017-12) 
        sec:5.4.2.1 eq:5.6 p:93 

    (local_test_press_unity)
    """
    p_lt_uty = (p_li - p_e) * α_spt / p_lt
    return p_lt_uty