Calculating equivalent resistance (R x || R y is the total resistance of two parallel resistors): R T h = R 1 + [ ( R 2 + R 3 ) ‖ ‖ R 4 ] = 1 k Ω Ω + [ ( 1 k Ω Ω + 1 k Ω Ω ) ‖ ‖ 2 k Ω Ω ] = 1 k Ω Ω + ( 1 ( 1 k Ω Ω + 1 k Ω Ω ) + 1 ( 2 k Ω Ω ) ) − − 1 = 2 k Ω Ω .