Following on from the discussion here, I measured operating pressure, fuel consumption and boil times for a No.1 stove and a 210, and got some interesting results! Experimental method I tried to compare apples with apples, so I chose two stoves with fairly unused burners, cleaned the pipes out on the burners (they were very clean anyway) and fitted replacement jets. The jets were both 0.32mm, as I squashed them in a vice until they were a push tight fit on a 0.32mm pricker. Incidentally the burner pipes have an OD of 6mm and 8mm, so significantly different. Then I measured the tank capacities by filling completely (tilting the tanks), and then filled each to ¾ capacity. The airscrew was removed from the No.1 and a flexible tube fitted with a Schrader valve at one end was connected over the airscrew pipe and over the air vent hole. The hose was connected securely over the air screw vent hole with a crimped hose clamp, which is not shown in this photo. A spare filler lid was used on the 210 with the air screw removed and a brass pipe brazed over the air hole. The Schrader valve and tube were connected as for the No.1. Before the tests both stoves and all the joints were leak tested under pressure by dunk tests. I did the tests on each stove one after the other, but the procedure was exactly the same. I fired up the stove as normal, then pumped to get a full throttle flame (about 20 pumps) and left the stove to stabilise for 5 mins. I then checked the pressure with the push on pressure gauge (0-60psi range) and then did the tea test, then checked the pressure again. I left each stove running for 15 mins total, then switched off, allowed them to cool and then drained the stove and check the fuel volume. The ‘tea test’ was done by putting 400ml of cold tap water into a cold MSR kettle, and measuring the time to achieve a rolling boil with the lid on. The lid was briefly lifted periodically to check when a rolling boil was achieved. The burner top to kettle bottom distance was the same in both cases. As you can see from the above flame shots, both burners were operating normally with no evidence of excess fuel/insufficient air mixing. Neither was there any soot on the kettle bottom after the tea tests. Results 210 Tank capacity was measured as 530cc, so the tank was filled with 400 cc for the tests. No.1 Tank capacity was measured as 2.125 pints (1200cc), so the tank was filled with 900 cc for the tests. Because I was so surprised by the low operating pressures... I decided to run the tests again without the pressure measuring connections which I thought may be leaking. I replaced the original filler caps and air screws so the stoves were as originally. I got the same results for boil tests and fuel consumption, so no leaks! Then I checked the pressure gauge for accuracy on my wife’s car tyres, which I had just pumped to 35psi at the gas station. Reading with my gauge 35psi! Errors My estimates are…. Error in boiling time measurements +/- 5 secs Error in fuel measurements is +/- 5cc Error in pressure is +/- 1psi Discussion Well, I am surprised at the low pressures and the fact that they are equal for both stoves. The fuel consumption data I measured are 160cc/hr for the 210 and 240cc/hr for the No. 1. This is similar to those reported by @kerophile here (193 and 279 respectively). The boil times for the No.1 are 30% faster than the 210 which is in line with reported power output differences. So why does the No.1 kick out more mass flow than the 210? PS When selecting the burners, I took the nipples out before cleaning the pipes, and after cleaning I blew through the burners with my mouth. The difference in resistance was very noticeable - even though the burners were relatively unused and clean. I still suspect that this is part of the answer.