How to distinguish a nearly flat Universe from a flat Universe using the orientation independence of a comoving standard ruler

Several recent observations using standard rulers and standard candles now suggest, either individually or in combination, that the Universe is close to flat, i.e. that the curvature radius is about as large as the horizon ra dius (similar to 10h(-1) Gpc) or larger. Here, a method of distinguishing a n almost Bat universe from a precisely flat universe using a single observa tional data set, without using: any microwave background information, is pr esented. The method (i) assumes that a standard ruler should have no prefer red orientation (radial versus tangeatial) to the observer, and (ii) requir es that the (comoving) length of the standard ruler be known independently (e.g. front low redshift estimates). The claimed feature at fixed comoving length in the power spectrum of density perturbations, detected among quasa rs: Lyman break galaxies or other high redshift objects, mould provide an a dequate standard candle to prove that the Universe is curved, if indeed it is curved. For example, a combined intrinsic and measurement uncertainty of 1% in the length of the standard ruler L applied at a redshift of z = 3 wo uld distinguish an hyperbolic (Omega (m) = 0.2, Omega (Lambda) = 0.7) or a spherical (Omega (m) = 0.4, Omega (Lambda) = 0.7) universe from a flat one to 1 - P > 95% confidence.