I would solve this problem by starting from the equation for a pendulum's period:
T ≈ 2π√( L / g )
Rearranging for g, and substituting the length in Cambridge:
g ≈ ( 4π² * L ) / T²
. . = ( 4π * 0.9942 m ) / ( 1.000 s + 1.000 s )²
. . = 9.812 m/s²
And for Tokyo:
g ≈ ( 4π² * L ) / T²
. . = ( 4π * 0.9927 m ) / ( 1.000 s + 1.000 s )²
. . = 9.798 m/s²
