The kūrma
The Śrī Yantra on a spherical cap — the tortoise-backed form.
Some texts describe the yantra not as flat but as raised on a dome, curved like a tortoise’s shell. That form has been used, for the better part of forty years, to explain why the plane figure is hard to draw: the argument runs that the true figure was spherical all along and the plane version is a degraded copy.
This platform takes the kūrma seriously as an object and rejects it as an explanation. Both halves of that matter, and they are separable.
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What follows the introduction is working material: the interactive dome you can turn and measure, the misfit curve across cap radii, a correction to the only published spherical formulation, and the proportions of the accurate kūrma. That is the platform, not the argument for it — and the platform is what a licence buys.
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The full argument is Part VI of the book: what the kūrma is, Rao’s formulation, what the sphere buys, testing the hypothesis, and the accurate kūrma.