def find_uts_ax_vlim(layers, vlims={}):
    """Find y axis limits for uts axes

    Parameters
    ----------
    layers : list of NDVar
        Data to be plotted.
    vlims : dict
        Vmax and vmin values by (meas, cmap).

    Returns
    -------
    bottom : None | scalar
        Lowest value on y axis.
    top : None | scalar
        Highest value on y axis.
    """
    bottom = None
    top = None
    for ndvar in layers:
        meas = ndvar.info.get('meas')
        if meas in vlims:
            bottom_, top_ = vlims[meas]
            if bottom is None:
                bottom = bottom_
            elif bottom_ != bottom:
                bottom = min(bottom, bottom_)
            if top is None:
                top = top_
            elif top_ != top:
                top = max(top, top_)
    return bottom, top
