diff --git a/src/riemann.rs b/src/riemann.rs
index 10556b8..dfeea72 100644
--- a/src/riemann.rs
+++ b/src/riemann.rs
@@ -15,7 +15,7 @@ pub trait Metric {
 	}
 
 	fn part_derivs_at(&self, pos: Vec3) -> Tens3 {
-		part_deriv(|p| self.at(p), pos, 1.0 / 1024.0) // division by such eps is exact which is good for overall precision
+		part_deriv(|p| self.at(p), pos, 1.0 / 64.0) // there just isn’t enough precision for a small ε.
 	}
 
 	fn vec_length_at(&self, at: Vec3, v: Vec3) -> f32 {