I agree and there are so many inter-related factors contributing to the efficiency and firing cycle of the springer. As we all know it's all a question of balance. However, the SCR can be a useful indicator in terms of efficiency. For example, the HW77 has a high SCR and is regarded as an efficient power plant. The B2, with its high TP volume as standard, benefits from a raising of the SCR via reducing the transfer port diameter, as Mick (T20) found.