//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
ll x[1001000],y[1001000];
ll l[1001000],r[1001000];
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int t;
	cin>>t;
	while(t--)
	{
		int n;
		cin>>n;
		for(int i=1;i<=n;i++)
			cin>>x[i]>>y[i];
		ll L=0,R=inf;
		while(L<R)
		{
			ll mid=(L+R)/2;
			for(int i=1;i<=n;i++)
				l[i]=r[i]=-1;
			l[1]=0;
			r[1]=inf;
			for(int i=2;i<=n;i++)
			{
				if(abs(y[i-1]-y[i])<=(x[i]-x[i-1])*mid)
				{
					l[i]=l[i-1]-(x[i]-x[i-1])*mid;
					r[i]=r[i-1]+(x[i]-x[i-1])*mid;
				}
				if(y[i]>=l[i-1]-(x[i]-x[i-1])*mid&&y[i]<=r[i-1]+(x[i]-x[i-1])*mid)
				{
					if(l[i]==-1)
					{
						l[i]=y[i-1]-(x[i]-x[i-1])*mid;
						r[i]=y[i-1]+(x[i]-x[i-1])*mid;
					}
					else
					{
						l[i]=min(l[i],y[i-1]-(x[i]-x[i-1])*mid);
						r[i]=max(r[i],y[i-1]+(x[i]-x[i-1])*mid);
					}
				}
			}
			if(l[n]!=-1)
				R=mid;
			else
				L=mid+1;
		}
		if(L==inf)
			cout<<"-1\n";
		else
			cout<<L<<'\n';
	}
	return 0;
}