diff --git a/command_prompt.py b/command_prompt.py
index b1cd71d..e3856c5 100644
--- a/command_prompt.py
+++ b/command_prompt.py
@@ -368,12 +368,20 @@ class Command_prompt(Label):
         if len(argv)==2:
             # no argument: set to toggle
             self.app.painter.set_grid(-1)
-        elif argv[2]=="on" or argv[2]=="1":
+        elif argv[2]=="on":
             self.app.painter.set_grid(1)
-        elif argv[2]=="off" or argv[2]=="0":
+        elif argv[2]=="off":
             self.app.painter.set_grid(0)
         else:
-            self.message="error: unrecognized argument '"+argv[2]+"' -- usage 'set grid [on|off]'"
+            try:
+                mesh=float(argv[2])
+            except:
+                self.message="error: unrecognized argument '"+argv[2]+"' -- usage 'set grid [on|off|<float>]'"
+                return
+            if mesh<0:
+                self.message="error: grid size cannot be negative: '"+argv[2]+"'"
+                return
+            self.app.painter.set_grid(mesh)
             
 
 
diff --git a/painter.py b/painter.py
index 8546c43..d54b314 100644
--- a/painter.py
+++ b/painter.py
@@ -55,27 +55,27 @@ class Painter(Widget):
         with self.canvas:
             # draw grids
             for particle in self.particles:
-                if particle.grid:
-                    self.draw_grid(particle.squares[0].pos)
+                if particle.grid>0:
+                    self.draw_grid(particle.squares[0].pos,particle.grid)
 
             for particle in self.particles:
                 particle.draw()
 
-    def draw_grid(self,pos):
+    def draw_grid(self,pos,mesh):
         # height offset due to status bar and command prompt
         height_offset=self.app.status_bar.height+self.app.command_prompt.height
         # vertical lines
         # offest wrt 0
-        offset=(pos.x-0.5)%1
-        for i in range(math.floor(self.width/Square_element.size-offset)+1):
+        offset=(pos.x-mesh/2)%mesh
+        for i in range(math.floor((self.width/Square_element.size-offset)/mesh)+1):
             Color(1,1,1)
-            Line(points=((i+offset)*Square_element.size,height_offset,(i+offset)*Square_element.size,self.height+height_offset))
+            Line(points=((i*mesh+offset)*Square_element.size,height_offset,(i*mesh+offset)*Square_element.size,self.height+height_offset))
         # horizontal lines
         # offset wrt 0
-        offset=(pos.y-0.5)%1-height_offset/Square_element.size
-        for i in range(math.floor(self.height/Square_element.size-offset)+1):
+        offset=(pos.y-mesh/2)%1-height_offset/Square_element.size
+        for i in range(math.floor((self.height/Square_element.size-offset)/mesh)+1):
             Color(1,1,1)
-            Line(points=(0,(i+offset)*Square_element.size+height_offset,self.width,(i+offset)*Square_element.size+height_offset))
+            Line(points=(0,(i*mesh+offset)*Square_element.size+height_offset,self.width,(i*mesh+offset)*Square_element.size+height_offset))
 
 
     # respond to keyboard
@@ -280,15 +280,16 @@ class Painter(Widget):
         self.draw()
 
     # set grid for selected particles
-    # onoff: 1:on, 0:off, -1:toggle
-    def set_grid(self,onoff):
+    # set mesh to -1 to toggle on/off
+    def set_grid(self,mesh):
         for particle in self.selected:
-            if onoff==1:
-                particle.grid=True
-            elif onoff==0:
-                particle.grid=False
-            elif onoff==-1:
-                particle.grid=not particle.grid
+            if mesh==-1:
+                if particle.grid==0:
+                    particle.grid=1
+                else:
+                    particle.grid=-particle.grid
+            else:
+                particle.grid=mesh
         # redraw
         self.draw()
 
diff --git a/polyomino.py b/polyomino.py
index 7bfe366..1b5aa22 100644
--- a/polyomino.py
+++ b/polyomino.py
@@ -14,8 +14,8 @@ class Polyomino():
         self.color=kwargs.get("color",(0,0,1))
         self.selected=False
 
-        # whether to draw a background grid
-        self.grid=kwargs.get("grid",False)
+        # mesh of background grid (no grid for mesh size 0)
+        self.grid=kwargs.get("grid",0)
 
     # draw function
     def draw(self):