diff --git a/conf.lua b/conf.lua
index 400d160..6638c1e 100644
--- a/conf.lua
+++ b/conf.lua
@@ -36,7 +36,7 @@ function love.conf(t)
     t.modules.image = true              -- Enable the image module (boolean)
     t.modules.joystick = false          -- Enable the joystick module (boolean)
     t.modules.keyboard = true           -- Enable the keyboard module (boolean)
-    t.modules.math = false              -- Enable the math module (boolean)
+    t.modules.math = true               -- Enable the math module (boolean)
     t.modules.mouse = true              -- Enable the mouse module (boolean)
     t.modules.physics = false           -- Enable the physics module (boolean)
     t.modules.sound = false             -- Enable the sound module (boolean)
diff --git a/main.lua b/main.lua
index 6801a60..2b5422b 100644
--- a/main.lua
+++ b/main.lua
@@ -1,6 +1,9 @@
 require "run"
 
 local fps, frameTime, lastUpdate
+local fpsMax, fpsTimer, fluctuating, fpsSpeed
+
+local random, randomAmount, randomTime
 
 local speed, num, bars, width
 local WIDTH, HEIGHT
@@ -14,9 +17,11 @@ target FPS: %d (change with up/down arrow)
 actual FPS: %d
 speed: %d (change with left/right arrow)
 number of bars: %d (change with -/+)
-fullscreen: %s (toggle with f)
+fullscreen: %s (toggle with ctrl+f)
 busy wait: %s (toggle with b)
-vsync: %s (toggle with v+s)
+vsync: %s (toggle with s)
+fluctuating: %s (toggle with f, change max with ctrl + up/down arrow, change speed with ctrl + left/right arrow)
+random stutter: %s [%dms] (toggle with r, change max amount with ctrl + +/-, shift to change faster)
 
 Freesync will only work when the application is fullscreen on Linux.
 Busy waiting is more precise, but much heavier on processor and battery.
@@ -43,6 +48,16 @@ love.load = function()
 
     fps = flags.refreshrate - 5
     fps = (fps > 0) and fps or 56
+
+    fpsMax = fps
+    fpsTimer = 0
+    fluctuating = false
+    fpsSpeed = 10
+
+    random = false
+    randomTime = 0
+    randomAmount = 0
+
     frameTime = 1 / fps
     lastUpdate = 0
     speed = 10
@@ -59,34 +74,47 @@ love.load = function()
 
 end
 
-sanitize = function()
-    fps = math.max(1, fps)
-    frameTime = 1/fps
-
-    speed = math.max(1, speed)
-end
 
-
-love.update = function()
+love.update = function(dt)
 
     if love.busy then
-        while lastUpdate + frameTime > love.timer.getTime() do end
+        while lastUpdate + frameTime + randomTime > love.timer.getTime() do end
     else
-        while lastUpdate + frameTime > love.timer.getTime() do
+        while lastUpdate + frameTime + randomTime > love.timer.getTime() do
             love.timer.sleep(0.001)
         end
     end
     lastUpdate = love.timer.getTime()
 
+    fpsTimer = fpsTimer + dt * fpsSpeed / 10
+    if fluctuating then
+        fpsCur = fps + (math.sin(fpsTimer)/2 + 0.5) * (fpsMax - fps)
+        frameTime = 1/fpsCur
+    end
+
+    if random then
+        randomTime = (love.math.random() - 0.5 ) * randomAmount/1000
+    end
+
     for i = 1, num do
-        bars[i] = (bars[i] + speed / 10 * WIDTH * frameTime) % (WIDTH)
+        bars[i] = (bars[i] + speed * dt * WIDTH / 20) % (WIDTH)
     end
 end
 
 
 love.draw = function()
-
-    local str = string.format(str, fps, love.timer.getFPS(), speed, num, tostring(fullscreen), tostring(love.busy), tostring(vsync))
+    local fstr = fluctuating and ("true [max: %d, speed: %d, current: %d]"):format(fpsMax, fpsSpeed, fpsCur) or "false"
+
+    local str = string.format(str, 
+        fps,
+        love.timer.getFPS(),
+        speed,
+        num,
+        tostring(fullscreen),
+        tostring(love.busy),
+        tostring(vsync),
+        fstr,
+        tostring(random), randomAmount)
 
     for i = 1, num do
         love.graphics.rectangle("fill", bars[i], y, width, HEIGHT)
@@ -103,44 +131,77 @@ love.draw = function()
 end
 
 
+sanitize = function()
+    fps = math.max(1, fps)
+    frameTime = 1/fps
+    fpsMax = math.max(fpsMax, fps)
+    fpsSpeed = math.max(1, fpsSpeed)
+
+    randomAmount = math.max(math.min(randomAmount, 1000), 0)
+
+    speed = math.max(1, speed)
+end
+
 love.keypressed = function(key, keycode)
 
-    local s = love.keyboard.isDown("s")
-    local v = love.keyboard.isDown("v")
-
-    if key == "up" then
-        fps = fps + 1
-    elseif key == "down" then
-        fps = fps - 1
-    elseif key == "left" then
-        speed = speed - 1
-    elseif key == "right" then
-        speed = speed + 1
-    elseif key == "-" or key == "_" then
-        num = num - 1
-        num = math.max(1, num)
-        newBars()
-    elseif key == "=" or key == "+" then
-        num = num + 1
-        num = math.max(1, num)
-        newBars()
-    elseif key == "f" then
-        if fullscreen then
-            love.window.setFullscreen(false)
-            love.window.setPosition(1, 1)
-        else
-            love.window.setFullscreen(true)
-            love.window.setPosition(0, 0)
+    local ctrl = love.keyboard.isDown("lctrl", "rctrl")
+    local shift = love.keyboard.isDown("lshift", "rshift")
+
+    if ctrl then
+        if key == "up" then
+            fpsMax = fpsMax + 1
+        elseif key == "down" then
+            fpsMax = fpsMax - 1
+        elseif key == "left" then
+            fpsSpeed = fpsSpeed - 1
+        elseif key == "right" then
+            fpsSpeed = fpsSpeed + 1
+        elseif key == "+" then
+            randomAmount = randomAmount + (shift and 5 or 1)
+        elseif key == "-" then
+            randomAmount = randomAmount - (shift and 5 or 1)
+        elseif key == "f" then
+            if fullscreen then
+                love.window.setFullscreen(false)
+                love.window.setPosition(1, 1)
+            else
+                love.window.setFullscreen(true)
+                love.window.setPosition(0, 0)
+            end
+            fullscreen = not fullscreen
+        end
+    else
+        if key == "up" then
+            fps = fps + 1
+        elseif key == "down" then
+            fps = fps - 1
+        elseif key == "left" then
+            speed = speed - 1
+        elseif key == "right" then
+            speed = speed + 1
+        elseif key == "-" or key == "_" then
+            num = num - 1
+            num = math.max(1, num)
+            newBars()
+        elseif key == "=" or key == "+" then
+            num = num + 1
+            num = math.max(1, num)
+            newBars()
+        elseif key == "f" then
+            fluctuating = not fluctuating
+            fpsTimer = 0
+        elseif key == "b" then
+            love.busy = not love.busy
+        elseif key == "s" then
+            local w, h, flags = love.window.getMode()
+            flags.vsync = (flags.vsync == 0) and 1 or 0
+            love.window.setMode(w, h, flags)
+            flags = select(3, love.window.getMode())
+            vsync = flags.vsync > 0
+        elseif key == "r" then
+            random = not random
+            randomTime = 0
         end
-        fullscreen = not fullscreen
-    elseif key == "b" then
-        love.busy = not love.busy
-    elseif (key == "v" and s) or (key == "s" and v) then
-        local w, h, flags = love.window.getMode()
-        flags.vsync = (flags.vsync == 0) and 1 or 0
-        love.window.setMode(w, h, flags)
-        flags = select(3, love.window.getMode())
-        vsync = flags.vsync > 0
     end
     sanitize()
 end