How can you measure the height of a building, using a Barometer?
Some answers aren't very practical but they are still valid.

• Use the pressure difference at the top and bottom of the building to work out the height.(the common answer)
• Pendulum - Swing the barometer like a pendulum from the end of a long rope. Use the period to calculate the height. (if the period is 63.4 seconds how high is the building)
• Pendulum - Swing the barometer like a pendulum both on the ground and on the roof, and from the known pendulum length and swing period, calculate the gravitational field for the two cases. Use Newton's law of gravitation to calculate the radial altitude of both the ground and the roof. The difference will be the height of the building.
• Shadows - When the sun is shining, standing the barometer up, measuring the height of the barometer and the lengths of the shadows of both barometer and building, and finding the building's height using similar triangles.
• Extrapolation - Tie the Barometer to a thread. Go to the First Floor and release the thread through the window until it touches the Ground. Calculate how many "barometer lengths" make up the height of one floor, and multiply this by the number of floors.
• Gravity - drop the barometer off the roof, measuring the time it takes to hit the ground, and use SUVAT to calculate the building's height assuming constant acceleration under gravity.
• Competition - Offer the barometer as first prize in a 'guess the height of the building' competition.
• Linear measurement - Attach the barometer to the end of a long rope, climb the building, lower the barometer to the ground, then measure the length of the rope.