As I noted elsewhere, I installed cheap digital temperature gauges in my two cheap old machines (Krups Novo 2300, Saeco ViaVenezia). I had installed a dimmer in the Saeco some months ago, and yesterday I installed one in the Krups.

The shot I pulled on the Krups yesterday was delicious... and the one I just pulled on the Saeco is my best ever.

What I found is that the temperature gauge allows me to use the dimmer to adjust the flow, such that I can keep the boiler temperature somewhat consistent. For my full blast pre-shot flush (which also warms the head and portafilter) I watched the boiler temperature fall from over 200 to 153. When I pulled the shot, I let the temperature come back up to 202. I pre-infused, which gradually dropped the boiler to 196. Then I gradually pulled the shot. The gauge never fell below 191 until the last four seconds, when I ran it full blast. When I stopped the shot, the temperature had dropped to 186.

The gauge on the Saeco seems to be spot-on with the water in the boiler.

So... if you've installed a dimmer for flow control, be sure to also install an instant-read thermometer of some sort. Use it as your guide for manipulating the flow. I think that these things, along with total shot time, might be more important than grams in grams out.