Your work on measuring atmospheric pressure has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
When water goes up into the vertical tube the water in the pressure tube moves slightly towards the stopped end of the pressure tube.
I used the double reduction ruler because it seems to be the most resonable to use.
29
I laid the meniscus on 10 and found the end of the tube to be at 39 therefore the lenght is 29.
10 cm
29
10.0,10.3
9.9,10.2
9.9,10.2
9.8,10.1
9.8,10.0
20 cm
29
10.0,10.7
10.0,10.7
10.0,10.7
10.0,10.7
10.0,10.7
30 cm
29
10.0,11.0
10.0,10.9
10.0,10.9
10.0,11.0
10.0,10.9
Your data appear to be very good, and should produce good results.