The tangent of an angle is the ratio of the length of the leg of a right triangle opposite the angle divided by the length of the leg on which the angle sits (this leg is called the adjacent side). The angle sits between the adjacent side and the hypotenuse. No matter how big or small the right triangle is, this ratio, called the tangent of this particular angle, never changes; it’s a property of the angle. The tangent of 42° is about 0.9 or ⁹⁄₁₀. This means that if the leg opposite the 42° angle is 9cm long then the leg on which the angle sits is 10cm long. It also means that if the opposite leg was 90 feet long then the adjacent leg would be 100 feet long. And the same tangent would apply if the opposite leg was 27 inches long and the adjacent leg was 30 inches long, because 27÷30=9÷10 (the fraction reduces to the same decimal).
When the angle measures 45°, the opposite and adjacent legs are the same length, so the tangent of 45° is 1.