#include<bits/stdc++.h>
#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<set>
using namespace std;
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define per(i,a,b) for(int i=(a);i>=(b);--i)
typedef long long ll;
typedef double db;
typedef pair<ll,ll> P;
#define fi first
#define se second
#define pb push_back
#define dbg(x) cerr<<(#x)<<":"<<x<<" ";
#define dbg2(x) cerr<<(#x)<<":"<<x<<endl;
#define SZ(a) (int)(a.size())
#define sci(a) scanf("%d",&(a))
#define pt(a) printf("%d",a);
#define pte(a) printf("%d\n",a)
#define ptlle(a) printf("%lld\n",a)
#define debug(...) fprintf(stderr, __VA_ARGS__)
const int N=1e6+10,INF=1e9,mod=998244353;
int t,n,isl[N];
P a[N];
map<int,int>q;
bool ok2(ll v,ll x){
    ll now=-1,las=-1;
    per(i,n,1){
        if(a[i].se<=x || isl[i]){
            if(now==-1 || abs(a[i].se-now)<=1ll*v*abs(a[i].fi-las))now=a[i].se,las=a[i].fi;
            else return 0;
        }
    }
    return 1;
}
bool ok(ll v){
    ll l=1,r=1e9;
    while(l<=r){
        ll mid=(l+r)/2;
        if(ok2(v,mid))l=mid+1;
        else r=mid-1;
    }
    ll now=-1,las=-1;
    per(i,n,1){
        if(isl[i])continue;
        if(a[i].se>=l){
            if(now==-1 || abs(a[i].se-now)<=1ll*v*abs(a[i].fi-las))now=a[i].se,las=a[i].fi;
            else return 0;
        }
    }
    return 1;
}
ll sol(){
    sci(n);
    q.clear();
    bool no=0;
    rep(i,1,n){
        isl[i]=0;
        scanf("%lld%lld",&a[i].fi,&a[i].se);
        q[a[i].fi]++;
        if(q[a[i].fi]>=3)no=1;
    }  
    if(no)return -1;
    sort(a+1,a+n+1);
    rep(i,1,n){
        if(i+1<=n && a[i+1].fi==a[i].fi)isl[i]=1;
    }
    ll l=0,r=INF;
    while(l<=r){
        ll mid=(l+r)/2;
        if(ok(mid))r=mid-1;
        else l=mid+1;
    }
    if(l>INF)return -1;
    return l;
}
int main(){
    sci(t);
    while(t--){
        ptlle(sol());
    }
    return 0;
}