diff --git a/src/render.rs b/src/render.rs
index d7e077c..9fa34f4 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -1,6 +1,8 @@
 use ansi_term::Color::RGB;
 use crate::geom::Point;
 use crate::{Material as _, SimSnapshot, SimState};
+use crate::mat;
+use crate::sim::Cell;
 use crate::meas::AbstractMeasurement;
 use decorum::R64;
 use font8x8::{BASIC_FONTS, UnicodeFonts as _};
@@ -87,23 +89,26 @@ impl<'a> RenderSteps<'a> {
             }
         }
     }
-    fn render_e_field(&mut self) {
+    fn render_vector_field<F: Fn(&Cell<mat::Static>) -> Point>(&mut self, color: Rgb<u8>, measure: F) {
         let w = self.sim.width();
         let h = self.sim.height();
-        let evec_spacing = 10;
+        let vec_spacing = 10;
         for y in 0..h {
             for x in 0..w {
-                if x % evec_spacing == 0 && y % evec_spacing == 0 {
-                    let evec = self.e_vector(x, y, evec_spacing);
-                    let norm_vec = scale_vector(evec, 100.0);
-                    let alpha = scale_unsigned(evec.mag_sq(), 500.0);
-                    let vec = norm_vec * (evec_spacing as f64);
-                    let center = Point::new(x as _, y as _) + Point::new(evec_spacing as _, evec_spacing as _)*0.5;
-                    self.im.draw_field_arrow(center, vec, Rgb([0xff, 0xff, 0xff]), alpha as f32);
+                if x % vec_spacing == 0 && y % vec_spacing == 0 {
+                    let vec = self.field_vector(x, y, vec_spacing, &measure);
+                    let norm_vec = scale_vector(vec, 100.0);
+                    let alpha = scale_unsigned(vec.mag_sq(), 500.0);
+                    let vec = norm_vec * (vec_spacing as f64);
+                    let center = Point::new(x as _, y as _) + Point::new(vec_spacing as _, vec_spacing as _)*0.5;
+                    self.im.draw_field_arrow(center, vec, color, alpha as f32);
                 }
             }
         }
     }
+    fn render_e_field(&mut self) {
+        self.render_vector_field(Rgb([0xff, 0xff, 0xff]), |cell| cell.e());
+    }
     fn render_measurements(&mut self) {
         for (meas_no, m) in self.meas.iter().enumerate() {
             let meas_string = m.eval(self.sim);
@@ -124,8 +129,8 @@ impl<'a> RenderSteps<'a> {
         }
     }
 
-    fn e_vector(&self, xidx: u32, yidx: u32, size: u32) -> Point {
-        let mut e = Point::default();
+    fn field_vector<F: Fn(&Cell<mat::Static>) -> Point>(&self, xidx: u32, yidx: u32, size: u32, measure: &F) -> Point {
+        let mut field = Point::default();
         let w = self.sim.width();
         let h = self.sim.height();
         let xstart = xidx.min(w);
@@ -134,7 +139,7 @@ impl<'a> RenderSteps<'a> {
         let yend = (ystart + size).min(h);
         for y in ystart..yend {
             for x in xstart..xend {
-                e += self.sim.get(x, y).e();
+                field += measure(self.sim.get(x, y));
             }
         }
         let xw = xend - xstart;
@@ -143,7 +148,7 @@ impl<'a> RenderSteps<'a> {
             // avoid division by zero
             Point::new(0.0, 0.0)
         } else {
-            e * (1.0 / ((xw*yw) as f64))
+            field * (1.0 / ((xw*yw) as f64))
         }
     }
 }