#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define per(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
#define mid ((l+r)>>1)
using namespace std;
const int N=1e6+10,inf=0x3f3f3f3f;
int n,a[N],t[N],p[N];
bool checkk(int i,int j,int k){
    if(i==-1||j==-1) return 0;
    return !i||!j||1ll*abs(a[p[i]]-a[p[j]])<=1ll*k*abs(t[p[i]]-t[p[j]]);
}
bool f[N],dv[N];
bool check(int k){
    rep(i,2,n) dv[i]=checkk(i-1,i,k);
    f[0]=f[1]=f[2]=1;
    int l=2-dv[2],pl=1,pr=1;if(dv[2]) pl=pr=0;
    rep(i,3,n){
        f[i]=checkk(pl,i,k)|checkk(pr,i,k);
        if(!dv[i]) pl=pr=-1;
        if(f[i]){
            if(pl==-1||1ll*a[p[pl]]+1ll*t[p[pl]]*k>1ll*a[p[i-1]]+1ll*t[p[i-1]]*k) pl=i-1;
            if(pr==-1||1ll*a[p[pr]]+1ll*t[p[pr]]*k>1ll*a[p[i-1]]-1ll*t[p[i-1]]*k) pr=i-1;
        }
    }
    per(i,n,2){
        if(f[i]) return 1;
        if(!dv[i]) break;
    }
    return 0;
}
int main(){
    int T;scanf("%d",&T);while(T--){
        scanf("%d",&n);rep(i,1,n) scanf("%d%d",t+i,a+i);iota(p+1,p+n+1,1);sort(p+1,p+n+1,[&](int A,int B){return t[A]<t[B];});
        if(n<=2) {puts("0");continue;}
        int l=0,r=inf,res=inf+1;while(l<=r) check(mid)?res=mid,r=mid-1:l=mid+1;printf("%d\n",res==inf+1?-1:res);
    }
    return 0;
}