2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4263CMB angular spectrum measurements suggest a flat universe. This paper clarifies the relation between geometry and the spherical harmonic index of the first acoustic peak ($\ell_{peak}$). Numerical and analytic calculations show that $\ell_{peak}$ is approximately a function of $Ω_K/Ω_M$ where $Ω_K$ and $Ω_M$ are the curvature ($Ω_K > 0$ implies an open geometry) and mass density today in units of critical density. Assuming $Ω_K/Ω_M \ll 1$, one obtains a simple formula for $\ell_{peak}$, the derivation of which gives another perspective on the widely-recognized $Ω_M$-$Ω_Λ$ degeneracy in flat models. This formula for near-flat cosmogonies together with current angular spectrum data yields familiar parameter constraints.4 pages; submitted to ApJ LettersAstrophysicstext