JavaRanger wrote:What scale is that?

I think they are talking Fahrenheit. It is still used in the U.S.

Yes it's Greek to me too

JavaRanger wrote:What scale is that?

There are some $15 scales on Ebay with the desc "500g x 0.01g Digital Jewelry Scale 0.01 gram Precision Scale w/ Piece Counting".
Meh. It's OK. Slow to respond, but works. On/off button sometimes takes a 2nd press. It works like a 15 buck scale. May do the new Acaia scale down the road.

Ok so I did a quick experiment this weekend (with my own Pro 700).

First I bought myself a cheap digital meat thermometer. The thermometer is supposedly good from -40C to 230C. It displays to 0.5F when in Fahrenheit units but I have no idea about the actual precision. Plunged into a pan of boiling water it raised to 210F but perhaps 212F is only found at the bottom of the pan. So if anything, the thermometer may display a bit below the actual temperature around the boiling point, but it's probably fairly accurate. When placed side by side with our indoor digital thermometer the difference was about 0.2F, which is below the display precision of the meat thermometer anyway.

So with the Pro 700 at the default PID settings and a t1 of 200F, I used the overflowing cup method to measure the group output temperature. This method is a bit awkward. At first it takes a few seconds for the thermometer to heat up and stabilize. However since the flow is not restricted, lots of water goes through the group and after maybe 10 seconds the temperature starts to drop as fresh water is drawn into the brew boiler. So I wanted to see the hottest, peak temperature produced at the group output to gauge whether out of the box the temperature is set too high. With the overflowing cup method, water also has time to cool down a bit I guess, so the recorded temperature should be a low-ball estimate.

Using this method, the peak temperature was 204.5-205F. So it's probably above t1 by 5F, which is quite large and could explain, in parts, my troubles at producing shots that are not over-extracted. Now changing the offset temperature is the way to go but it's much simpler to change t1 during tests, so I brought t1 down in successive increments to 194F. It looks like as water cools down, it looses less heat through the group (because the temperature differential is lower I guess), and thus at t1 = 194F I'm still at 200.5-201F. Next step will probably be, as Eric suggested, to set the offset to 0 and adjust t1 to get 200F (or even lower I guess for ligther roasts?) at the group ouput.

It didn't solve everything but it does look to me as if I have more leeway to adjust a shot's taste between sour/acidic and bitter with this temperature.