You can calculate it with such a simple experiment as dropping a bullet from 20 meters height and measure the time.
You do this experiment on the pole and the equator and you get differant results.
So what equipment do I need? a superaccurate clock and a nice vacuum pipe to drop the bullet in.
I ofcourse have not been to the pole and equator and done this, but i tried it in Sweden, using a little more sophisticated methods
(A ball dropping and having a instrument given to me by school [OMG NO CONSIRACY] and pluggin it to a computer, getting some nice scales on excel) and getting a number matching with the list I found on wikipedia:
Amsterdam 9.813 m/s² Istanbul 9.808 m/s² Paris 9.809 m/s²
Athens 9.807 m/s² Havana 9.788 m/s² Rio de Janeiro 9.788 m/s²
Auckland, NZ 9.799 m/s² Helsinki 9.819 m/s² Rome 9.803 m/s²
Bangkok 9.783 m/s² Kuwait 9.793 m/s² San Francisco 9.800 m/s²
Brussels 9.811 m/s² Lisbon 9.801 m/s² Singapore 9.781 m/s²
Buenos Aires9.797 m/s² London 9.812 m/s²Stockholm 9.818 m/s²
Calcutta 9.788 m/s² Los Angeles9.796 m/s² Sydney 9.797 m/s²
Cape Town 9.796 m/s² Madrid 9.800 m/s² Taipei 9.790 m/s²
Chicago 9.803 m/s² Manila 9.784 m/s² Tokyo 9.798 m/s²
Copenhagen9.815 m/s² Mexico City 9.779 m/s² Vancouver, BC 9.809 m/s²
Nicosia 9.797 m/s² New York 9.802 m/s² Washington, DC 9.801 m/s²
Jakarta 9.781 m/s² Oslo 9.819 m/s² Wellington, NZ 9.803 m/s²
Frankfurt 9.810 m/s² Ottawa 9.806 m/s² Zurich 9.807 m/s²