def jog_on(a, b):
    if not manual_ok(): return
    if not manual_tab_visible(): return
    c.teleop_enable(1)
    if isinstance(a, (str, unicode)):
        a = "xyzabcuvw".index(a)
    if a < 3:
        if vars.metric.get(): b = b / 25.4
        b = from_internal_linear_unit(b)
    if jog_after[a]:
        root_window.after_cancel(jog_after[a])
        jog_after[a] = None
        return
    jogincr = widgets.jogincr.get()
    if jogincr != _("Continuous"):
        s.poll()
        if s.state != 1: return
        distance = parse_increment(jogincr)
        jog(linuxcnc.JOG_INCREMENT, a, b, distance)
        jog_cont[a] = False
    else:
        jog(linuxcnc.JOG_CONTINUOUS, a, b)
        jog_cont[a] = True
        jogging[a] = b