What is the best way to measure many copies of a light beam? An Evidence Press briefing. Many precision experiments read a tiny change in a beam of light by measuring its electric field with a technique called homodyne detection. If you can prepare the same beam several times, you can measure each copy on its own, or combine the copies first. Quantum theory says the information from separate copies simply adds up. But if you restrict yourself to the standard optical toolbox, mirrors, beam splitters, squeezed light and homodyne detectors, combining the copies can do better. A 2025 paper by Navarro, Morelli, Sanz and Mehboudi showed this, using an interferometer that gathers the changing brightness of all the copies into one output beam, while the other outputs keep only the changing noise. They left open whether that is the best possible scheme for a small number of copies. This release settles the question for every pure single-beam Gaussian state. No measurement built from the standard toolbox, even with extra auxiliary light, beats the simple scheme: gather the signal into one bright output, measure that output at one well chosen angle, and measure every other output along a fixed direction. The best achievable information is given by a short formula. The paper also gives the exact answer when the measurement may use only limited squeezing, and shows that the total shortfall from the quantum limit stays below the noise information of a single copy, however many copies are used. Joint measurement helps exactly when the beam's brightness and its noise change in misaligned directions. The results have written proofs and numerical checks. The interferometer itself is due to the earlier paper; the new part is the proof that nothing beats it. This is an anonymous, AI-assisted, unrefereed candidate, not peer reviewed or independently reproduced. Published on 31 October 2026, its paper and evidence are linked from the Evidence Press release page. This briefing uses an AI-generated voice and is not additional scientific evidence.