  The $^1\mathrm{S}_0$-$^3\mathrm{P}_0$ clock transition frequency
$\nu_\text{Sr}$ in neutral $^{87}$Sr has been measured relative to the Cs
standard by three independent laboratories in Boulder, Paris, and Tokyo over
the last three years. The agreement on the $1\times 10^{-15}$ level makes
$\nu_\text{Sr}$ the best agreed-upon optical atomic frequency. We combine
periodic variations in the $^{87}$Sr clock frequency with $^{199}$Hg$^+$ and
H-maser data to test Local Position Invariance by obtaining the strongest
limits to date on gravitational-coupling coefficients for the fine-structure
constant $\alpha$, electron-proton mass ratio $\mu$ and light quark mass.
Furthermore, after $^{199}$Hg$^+$, $^{171}$Yb$^+$ and H, we add $^{87}$Sr as
the fourth optical atomic clock species to enhance constraints on yearly drifts
of $\alpha$ and $\mu$.
