diff --git a/mortie/tests/test_tools.py b/mortie/tests/test_tools.py
index d8cdfea..2f1f0aa 100644
--- a/mortie/tests/test_tools.py
+++ b/mortie/tests/test_tools.py
@@ -45,6 +45,56 @@ def test_order2res_decreasing(self):
         assert all(resolutions[i] > resolutions[i+1] for i in range(len(resolutions)-1))
 
 
+class TestRes2Display:
+    """Test the resolution-ladder printer"""
+
+    def test_prints_all_orders_through_max(self, capsys):
+        """One line per order 0..MAX_ORDER -- no silent drop above 19"""
+        tools.res2display()
+        lines = capsys.readouterr().out.strip().split('\n')
+        assert len(lines) == tools.MAX_ORDER + 1
+        # every order 0..29 appears with its trailing phrasing
+        for order in range(tools.MAX_ORDER + 1):
+            assert any(
+                line.endswith('at tessellation order ' + str(order))
+                for line in lines
+            )
+
+    def test_max_order_argument(self, capsys):
+        """max_order bounds the printed range inclusively"""
+        tools.res2display(max_order=5)
+        lines = capsys.readouterr().out.strip().split('\n')
+        assert len(lines) == 6
+        assert lines[-1].endswith('at tessellation order 5')
+
+    def test_unit_ladder_km_m_cm(self, capsys):
+        """Coarse orders read in km, sub-km in m, sub-m in cm"""
+        tools.res2display()
+        lines = capsys.readouterr().out.strip().split('\n')
+        by_order = {int(line.rsplit(' ', 1)[1]): line for line in lines}
+        # order 12 = 1.589 km, order 13 = 794.456 m (the issue's examples)
+        assert by_order[12] == '1.589 km at tessellation order 12'
+        assert by_order[13] == '794.456 m at tessellation order 13'
+        # finest orders drop to cm rather than tiny km/m fractions
+        assert by_order[25] == '19.396 cm at tessellation order 25'
+        assert by_order[29] == '1.212 cm at tessellation order 29'
+
+    def test_rounds_within_bracket(self, capsys):
+        """Values are rounded to three decimals inside the chosen unit"""
+        tools.res2display()
+        lines = capsys.readouterr().out.strip().split('\n')
+        for line in lines:
+            number = line.split(' ', 1)[0]
+            # at most three digits after the decimal point
+            assert '.' in number and len(number.split('.')[1]) <= 3
+
+    def test_out_of_range_raises(self):
+        """max_order outside 0..MAX_ORDER is rejected"""
+        for bad in (-1, tools.MAX_ORDER + 1):
+            with pytest.raises(ValueError, match="max_order must be"):
+                tools.res2display(max_order=bad)
+
+
 class TestUnique2Parent:
     """Test UNIQ to parent cell conversion"""
 
diff --git a/mortie/tools.py b/mortie/tools.py
index c31108a..3c80971 100644
--- a/mortie/tools.py
+++ b/mortie/tools.py
@@ -24,10 +24,33 @@ def order2res(order):
     return res
 
 
-def res2display():
-    '''prints resolution levels'''
-    for res in range(20):
-        print(str(order2res(res)) + ' km at tessellation order ' + str(res))
+def res2display(max_order=MAX_ORDER):
+    '''prints resolution levels
+
+    Prints one line per tessellation order from 0 through ``max_order``
+    (default MAX_ORDER = 29, the finest order the packed-u64 kernel reaches).
+    Each resolution is rendered in the largest sensible unit -- km at coarse
+    orders, m once it drops below 1 km, cm once it drops below 1 m -- and
+    rounded to three decimals within that bracket, so fine orders read
+    naturally (e.g. order 12 -> ``1.589 km``, order 13 -> ``794.456 m``)
+    rather than as tiny km fractions.
+
+    ``max_order`` must lie in 0..MAX_ORDER, the order range the packed-u64
+    kernel encodes.
+    '''
+    if not 0 <= max_order <= MAX_ORDER:
+        raise ValueError(
+            f"max_order must be between 0 and {MAX_ORDER}, got {max_order!r}")
+    for res in range(max_order + 1):
+        km = order2res(res)
+        if km >= 1.0:
+            value, unit = km, 'km'
+        elif km >= 1e-3:
+            value, unit = km * 1e3, 'm'
+        else:
+            value, unit = km * 1e5, 'cm'
+        print(str(round(value, 3)) + ' ' + unit +
+              ' at tessellation order ' + str(res))
 
 
 def unique2parent(unique):