Manasara 46.17

46.17

madhyāttu bhrāmayecchilpī vṛttākāraṃ ca toraṇam
tadardhe nāsikādau tad bhrāmayedarthacandrakam

The artisan-architect should swing [the compass] from the center for a circular archway; / at its half, beginning from the gable dormer, he should swing the crescent [shape];