Critical energy values of benzylpyridinium ions are still rather high and do not always allow for reconstructing a nice survival yield curve in the softest ion production and ion transfer conditions. Several groups proposed new classes of thermometer ions with lower threshold energies, yet with the same advantages as the benzylpyridinium ions, such as a predominant simple bond cleavage fragmentation pathway, and a set of substituted molecules with similar masses, structures and numbers of degrees of freedom.