diff --git a/packages/ludic.nav/README.md b/packages/ludic.nav/README.md
index 0f6eba1f..70d99108 100644
--- a/packages/ludic.nav/README.md
+++ b/packages/ludic.nav/README.md
@@ -51,7 +51,7 @@ import "ludic.nav"
 | `nav_next_corner(kind, filter, sx, sy, sz, ex, ey, ez) -> bool` | the next corner of that way, read back as the nearest point is (a walker's one question a frame) |
 | `nav_straight(kind, filter, sx, sy, sz, ex, ez) -> bool` | does the straight line stay walkable |
 | `nav_random_near(kind, filter, x, y, z, r, seed) -> bool`, `nav_near_x/y/z()` | a reachable point about r away, from the caller's seed |
-| `nav_asked()`, `nav_found()`, `nav_short()` | paths asked for, found and cut short since the meshes loaded (a game's measure of how often its walkers had a way) |
+| `nav_asked()`, `nav_found()`, `nav_short()`, `nav_us()` | paths asked for, found and cut short since the meshes loaded, and the microseconds they took (timed in the shim by the OS clock: a game's measure of how often its walkers had a way, and what it cost) |
 | `nav_area_cost(kind, filter, area, cost)` | how dear a kind of ground is to cross by that filter |
 
 ## Tests
diff --git a/packages/ludic.nav/lib/macos-arm64/libludicnav.dylib b/packages/ludic.nav/lib/macos-arm64/libludicnav.dylib
index 3941b8a7..7d84075a 100755
--- a/packages/ludic.nav/lib/macos-arm64/libludicnav.dylib
+++ b/packages/ludic.nav/lib/macos-arm64/libludicnav.dylib
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:10555b7baa5958700f0ce4599e85fc4fc18b9c92afbbacfa64f04b630f42f583
-size 176816
+oid sha256:969c1ee0010c0fe88abcdfceb1a166031a8f6519b9e77a27c27331cbe2036e0b
+size 176912
diff --git a/packages/ludic.nav/lib/windows-x64/ludicnav.dll b/packages/ludic.nav/lib/windows-x64/ludicnav.dll
index 7a9c6695..0bdc9341 100644
--- a/packages/ludic.nav/lib/windows-x64/ludicnav.dll
+++ b/packages/ludic.nav/lib/windows-x64/ludicnav.dll
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:99671e7df79802010fbf132f736d1b5e2681f0cd72ab71e3aa6e7026b837c97c
-size 337408
+oid sha256:0ef49349d93dbc3b94c3743f80fa56f2acf4f5e02f16faba6ec13823b5705aaa
+size 337920
diff --git a/packages/ludic.nav/lib/windows-x64/ludicnav.lib b/packages/ludic.nav/lib/windows-x64/ludicnav.lib
index 9e1bdfe3..6bcfe136 100644
--- a/packages/ludic.nav/lib/windows-x64/ludicnav.lib
+++ b/packages/ludic.nav/lib/windows-x64/ludicnav.lib
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:c3e4f7ae19a6113829feffe2ed99e4a8f6b8fb2831c90115f489d1ecf646216a
-size 3866
+oid sha256:0ea766bfe59613b41a1566f41de772d49602191ad7e188bef3bcf453c55d6114
+size 4022
diff --git a/packages/ludic.nav/native.ludic b/packages/ludic.nav/native.ludic
index 71d02ce1..190af731 100644
--- a/packages/ludic.nav/native.ludic
+++ b/packages/ludic.nav/native.ludic
@@ -11,6 +11,7 @@ extern function nvc_nearest(h: pointer, x: float, y: float, z: float, out: point
 extern function nvc_area_cost(h: pointer, f: int, area: int, cost: float) -> void = "nav_area_cost"
 extern function nvc_path(h: pointer, f: int, sx: float, sy: float, sz: float, ex: float, ey: float, ez: float, out: pointer, max: int) -> int = "nav_path"
 extern function nvc_partial(h: pointer) -> int = "nav_partial"
+extern function nvc_us(h: pointer) -> int = "nav_us"
 extern function nvc_raycast(h: pointer, f: int, sx: float, sy: float, sz: float, ex: float, ez: float) -> int = "nav_raycast"
 extern function nvc_random_near(h: pointer, f: int, x: float, y: float, z: float, r: float, seed: int, out: pointer) -> int = "nav_random_near"
 extern function nvc_stage(size: int) -> pointer = "nav_stage"
diff --git a/packages/ludic.nav/native/shim/nav_query.inl b/packages/ludic.nav/native/shim/nav_query.inl
index c3a8fdf3..9eb476a6 100644
--- a/packages/ludic.nav/native/shim/nav_query.inl
+++ b/packages/ludic.nav/native/shim/nav_query.inl
@@ -22,8 +22,7 @@ NAV_SHIM void nav_area_cost(void *h, int f, int area, float cost) {
 // the corners of a path from one point to another, at most max of them, into out: the count, or
 // -1 when either end is off the mesh. One that cannot reach the end stops as near it as the mesh
 // allows, and nav_partial says so
-NAV_SHIM int nav_path(void *h, int f, float sx, float sy, float sz, float ex, float ey, float ez, float *out, int max) {
-  Nav *n = static_cast<Nav *>(h);
+static int nav_path_in(Nav *n, int f, float sx, float sy, float sz, float ex, float ey, float ez, float *out, int max) {
   float s[3] = {sx, sy, sz}, e[3] = {ex, ey, ez}, so[3], eo[3];
   dtPolyRef a = nav_poly_at(n, s, so), b = nav_poly_at(n, e, eo);
   n->partial = 0;
@@ -39,6 +38,15 @@ NAV_SHIM int nav_path(void *h, int f, float sx, float sy, float sz, float ex, fl
   if (dtStatusFailed(n->query->findStraightPath(so, end, n->polys, np, out, nullptr, nullptr, &count, max, 0))) return -1;
   return count;
 }
+NAV_SHIM int nav_path(void *h, int f, float sx, float sy, float sz, float ex, float ey, float ez, float *out, int max) {
+  Nav *n = static_cast<Nav *>(h);
+  long long t0 = nav_now_ns();
+  int r = nav_path_in(n, f, sx, sy, sz, ex, ey, ez, out, max);
+  n->ns += nav_now_ns() - t0;
+  return r;
+}
+// microseconds this mesh has spent finding paths
+NAV_SHIM int nav_us(void *h) { return static_cast<int>(static_cast<Nav *>(h)->ns / 1000); }
 NAV_SHIM int nav_partial(void *h) { return static_cast<Nav *>(h)->partial; }
 
 // does the straight line from one point to another stay on the mesh? 1 yes, 0 no, -1 off it
diff --git a/packages/ludic.nav/native/shim/nav_shim.cpp b/packages/ludic.nav/native/shim/nav_shim.cpp
index 4d5b485f..7710e6cb 100644
--- a/packages/ludic.nav/native/shim/nav_shim.cpp
+++ b/packages/ludic.nav/native/shim/nav_shim.cpp
@@ -17,7 +17,27 @@
 #define NAV_SHIM extern "C" __attribute__((visibility("default")))
 #endif
 
+#ifdef _WIN32
+extern "C" __declspec(dllimport) int __stdcall QueryPerformanceCounter(long long *);
+extern "C" __declspec(dllimport) int __stdcall QueryPerformanceFrequency(long long *);
+#else
+#include <time.h>
+#endif
+
 namespace {
+// a monotonic clock in nanoseconds, from the OS alone (KERNEL32 on Windows: no C++ runtime to ship)
+long long nav_now_ns() {
+#ifdef _WIN32
+  long long c = 0, f = 1;
+  QueryPerformanceCounter(&c);
+  QueryPerformanceFrequency(&f);
+  return (long long)((double)c * 1e9 / (double)f);
+#else
+  struct timespec t;
+  clock_gettime(CLOCK_MONOTONIC, &t);
+  return (long long)t.tv_sec * 1000000000LL + t.tv_nsec;
+#endif
+}
 const int NAV_MAX_POLYS = 512;     // polygons a path may cross; a longer one is cut there
 const int NAV_MAX_NODES = 4096;    // the search's open list
 const int NAV_FILTERS = 8;         // costs per kind of ground: one set per kind of walker's taste
@@ -30,6 +50,7 @@ struct Nav {
   float ext[3] = {2.0f, 4.0f, 2.0f};   // how far to look for the mesh around a point
   dtPolyRef polys[NAV_MAX_POLYS];
   int partial = 0;                     // the last path stopped short of its end
+  long long ns = 0;                    // time spent finding paths, for the measure (17.10)
 };
 
 // a navmesh with its query, from params (a set of tiles) or from one tile's data
diff --git a/packages/ludic.nav/query.ludic b/packages/ludic.nav/query.ludic
index 21e6ef6f..4733d3fd 100644
--- a/packages/ludic.nav/query.ludic
+++ b/packages/ludic.nav/query.ludic
@@ -47,6 +47,15 @@ export function nav_path(nav_st: mut NavState, kind: int, filter: int, sx: float
 export function nav_asked(nav_st: NavState) -> int { return nav_st.nv_asked }
 export function nav_found(nav_st: NavState) -> int { return nav_st.nv_found }
 export function nav_short(nav_st: NavState) -> int { return nav_st.nv_short }
+# microseconds spent finding those paths, over every loaded mesh
+export function nav_us(nav_st: NavState) -> int {
+  var us = 0
+  for k in 0 .. NAV_KINDS {
+    let h = nv_mesh(nav_st, k)
+    if h != null { us += nvc_us(h) }
+  }
+  return us
+}
 export function nav_partial(nav_st: NavState, kind: int) -> bool {
   let h = nv_mesh(nav_st, kind)
   return h != null and nvc_partial(h) == 1
diff --git a/packages/ludic.nav/tests/nav_test.ludic b/packages/ludic.nav/tests/nav_test.ludic
index cfc66f08..d17435db 100644
--- a/packages/ludic.nav/tests/nav_test.ludic
+++ b/packages/ludic.nav/tests/nav_test.ludic
@@ -124,4 +124,14 @@ program NavTest {
     nav_reset(nav_st)
     expect_eq(nav_polygons(nav_st, NAV_SMALL), 0)
   }
+
+  test "the time paths take is counted, and only while a mesh is loaded" (nav_st: mut NavState) {
+    expect_eq(nav_us(nav_st), 0)
+    expect(meadow(nav_st, NAV_PERSON, 0, true))
+    for i in 0 .. 2000 { nav_path(nav_st, NAV_PERSON, 0, 5.0, 0.0, 20.0, 35.0, 0.0, 20.0) }
+    expect(nav_us(nav_st) > 0)
+    expect(nav_us(nav_st) < 2000000)
+    nav_reset(nav_st)
+    expect_eq(nav_us(nav_st), 0)
+  }
 }