from decimal import Decimal

read_ints = lambda : map(int, raw_input().split())

def valid(transmitters, D):
    a = transmitters[0][1] - D
    b = transmitters[0][1] + D
    t = transmitters[0][0]
    for T, P in transmitters[1:]:
        A = P - D
        B = P + D

        l = abs(T - t)

        if A > b + l:
            return False
        if B < a - l:
            return False

        t = T
        a = max(A, a - l)
        b = min(B, b + l)
        assert a <= b

    return True


def solve():
    N = read_ints()[0]

    transmitters = []
    for n in range(N):
        P, T = read_ints()
        transmitters.append((Decimal(T), Decimal(P)))
    transmitters.sort()

    lower = Decimal(0)
    upper = max(t[0] for t in transmitters) - min(t[0] for t in transmitters)

    #i = 0
    #while not valid(transmitters, i):
    #    i += 1

    while upper - lower > Decimal(1) ** (-10):
        mid = lower + (upper - lower) / Decimal(2)

        if valid(transmitters, mid):
            upper = mid
        else:
            lower = mid

    return str(lower)

N = read_ints()[0]
for n in range(1, N+1):
    print 'Case #%d: %s' % (n, solve())