#include <bits/stdc++.h>
#define _rep(i, x, y) for(int i = x; i <= y; ++i)
#define _req(i, x, y) for(int i = x; i >= y; --i)
#define _rev(i, u) for(int i = head[u]; i; i = e[i].nxt)
#define pb push_back
#define fi first
#define se second
#define mst(f, i) memset(f, i, sizeof f)
using namespace std;
#ifdef ONLINE_JUDGE
#define debug(...) 0
#else
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#endif
typedef long long ll;
typedef pair<int, int> PII;
namespace fastio{
    #ifdef ONLINE_JUDGE
    char ibuf[1 << 20],*p1 = ibuf, *p2 = ibuf;
    #define get() p1 == p2 && (p2 = (p1 = ibuf) + fread(ibuf, 1, 1 << 20, stdin), p1 == p2) ? EOF : *p1++
    #else
    #define get() getchar()
    #endif
    template<typename T> inline void read(T &t){
        T x = 0, f = 1;
        char c = getchar();
        while(!isdigit(c)){
            if(c == '-') f = -f;
            c = getchar();
        }
        while(isdigit(c)) x = x * 10 + c - '0', c = getchar();
        t = x * f;
    }
    template<typename T, typename ... Args> inline void read(T &t, Args&... args){
        read(t);
        read(args...);
    }
    template<typename T> void write(T t){
        if(t < 0) putchar('-'), t = -t;
        if(t >= 10) write(t / 10);
        putchar(t % 10 + '0');
    }
    template<typename T, typename ... Args> void write(T t, Args... args){
        write(t), putchar(' '), write(args...);
    }
    template<typename T> void writeln(T t){
        write(t);
        puts("");
    }
    template<typename T> void writes(T t){
        write(t), putchar(' ');
    }
    #undef get
};
using namespace fastio;
#define multitest() int T; read(T); _rep(tCase, 1, T)
namespace Calculation{
    const ll mod = 998244353;
    ll ksm(ll p, ll h){ll base = p % mod, res = 1; while(h){if(h & 1ll) res = res * base % mod; base = base * base % mod, h >>= 1ll;} return res;}
    void dec(ll &x, ll y){x = ((x - y) % mod + mod) % mod;}
    void add(ll &x, ll y){x = (x + y) % mod;}
    void mul(ll &x, ll y){x = x * y % mod;}
    ll sub(ll x, ll y){return ((x - y) % mod + mod) % mod;}
    ll pls(ll x, ll y){return ((x + y) % mod + mod) % mod;}
    ll mult(ll x, ll y){return x * y % mod;}
}
using namespace Calculation;
const int N = 3e5 + 5;
typedef long double lb;
const lb eps = 1e-10;
ll n, a[N], L[N], R[N];
lb pre[N], suf[N];
bool check(lb mid){
    _rep(i, 1, n) pre[i] = pre[i - 1] + (lb)a[i] - mid;
    _req(i, n, 1) suf[i] = suf[i + 1] + (lb)a[i] - mid;
    int pos = 0;
    _rep(i, 2, n - 1){
        if(!L[i] || !R[i]) continue;
        pos = i;
        break;
    }
    lb minx = 0;
    _rep(i, 0, pos - 2) minx = min(minx, pre[i]);
    lb res = pre[pos - 1] + suf[pos + 1] + (lb)a[pos] - mid;
    res -= minx;
    minx = 0;
    _rep(i, pos + 2, n) minx = min(minx, suf[i]);
    res -= minx;
    if(res > -eps) return 1;
    return 0;
}
int main(){
    multitest(){
        read(n);
        _rep(i, 1, n) read(a[i]);
        _rep(i, 2, n){
            if(a[i] < a[i - 1]) L[i] = !L[i - 1] ? i - 1 : L[i - 1];
            else L[i] = 0;
        }
        _req(i, n - 1, 1){
            if(a[i] < a[i + 1]) R[i] = !R[i + 1] ? i + 1 : R[i + 1];
            else R[i] = 0;
        }
        lb l = 0, r = 1e15, res = 0;
        while(r - l > eps){
            lb mid = (l + r) / 2.00;
            if(check(mid)) l = mid + eps, res = mid;
            else r = mid - eps;
        }
        printf("%.10Lf\n", res);
    }
    return 0;
}