Mj    Mean anomaly of Jupiter
    Ms    Mean anomaly of Saturn

Perturbations for Jupiter. Add these terms to the longitude:
    -0.332 * sin(2*Mj - 5*Ms - 67.6 degrees)
    -0.056 * sin(2*Mj - 2*Ms + 21 degrees)
    +0.042 * sin(3*Mj - 5*Ms + 21 degrees)
    -0.036 * sin(Mj - 2*Ms)
    +0.022 * cos(Mj - Ms)
    +0.023 * sin(2*Mj - 3*Ms + 52 degrees)
    -0.016 * sin(Mj - 5*Ms - 69 degrees)

Perturbations for Saturn. Add these terms to the longitude:
    +0.812 * sin(2*Mj - 5*Ms - 67.6 degrees)
    -0.229 * cos(2*Mj - 4*Ms - 2 degrees)
    +0.119 * sin(Mj - 2*Ms - 3 degrees)
    +0.046 * sin(2*Mj - 6*Ms - 69 degrees)
    +0.014 * sin(Mj - 3*Ms + 32 degrees)

For Saturn: also add these terms to the latitude:
    -0.020 * cos(2*Mj - 4*Ms - 2 degrees)
    +0.018 * sin(2*Mj - 6*Ms - 49 degrees)

The "great Jupiter-Saturn term" is the largest perturbation for both Jupiter and Saturn. Its period is 918 years, and its amplitude is 0.332 degrees for Jupiter and 0.812 degrees for Saturn. The other perturbations have periods between 14 and 100 years. One should also mention the "great Uranus-Neptune term", which has a period of 4220 years and an amplitude of about one degree.