diff --git a/lib/tiny-debug.lua b/lib/tiny-debug.lua
new file mode 100644
index 0000000..6aaec92
--- /dev/null
+++ b/lib/tiny-debug.lua
@@ -0,0 +1,6 @@
+getCurrentTimeMilliseconds = playdate.getCurrentTimeMilliseconds
+
+tinyTrackEntityAges = true
+ENTITY_INIT_MS = { "ENTITY_INIT_MS" }
+
+tinyLogSystemUpdateTime = false
\ No newline at end of file
diff --git a/lib/tiny.lua b/lib/tiny.lua
index ce305a6..ef29000 100644
--- a/lib/tiny.lua
+++ b/lib/tiny.lua
@@ -484,9 +484,20 @@ function tiny.addEntity(world, entity)
 end
 tiny_addEntity = tiny.addEntity
 
+if tinyTrackEntityAges then
+    local wrapped = tiny.addEntity
+    function tiny.addEntity(world, entity)
+        local added = wrapped(world, entity)
+        added[ENTITY_INIT_MS] = getCurrentTimeMilliseconds()
+    end
+    tiny_addEntity = tiny.addEntity
+end
+
 --- Adds a System to the world. Returns the System.
 function tiny.addSystem(world, system)
-    assert(system.world == nil, "System already belongs to a World.")
+    if system.world ~= nil then
+        error("System " .. system.name .. " already belongs to a World.")
+    end
     local s2a = world.systemsToAdd
     s2a[#s2a + 1] = system
     system.world = world
@@ -521,7 +532,9 @@ tiny_removeEntity = tiny.removeEntity
 
 --- Removes a System from the world. Returns the System.
 function tiny.removeSystem(world, system)
-    assert(system.world == world, "System does not belong to this World.")
+    if system.world ~= world then
+        error("System " .. system.name .. " does not belong to this World.")
+    end
     local s2r = world.systemsToRemove
     s2r[#s2r + 1] = system
     return system
@@ -778,15 +791,15 @@ function tiny.update(world, dt, filter)
         end
     end
 
+    local tinyLogSystemUpdateTime = tinyLogSystemUpdateTime
     --  Iterate through Systems IN ORDER
     for i = 1, #systems do
         local system = systems[i]
         if system.active and ((not filter) or filter(world, system)) then
-            -- TODO: Track how long each system runs for during any given frame.
             -- Update Systems that have an update method (most Systems)
             local update = system.update
             if update then
-                --local currentMs = playdate.getCurrentTimeMilliseconds()
+                local currentMs = tinyLogSystemUpdateTime and getCurrentTimeMilliseconds()
                 local interval = system.interval
                 if interval then
                     local bufferedTime = (system.bufferedTime or 0) + dt
@@ -798,14 +811,18 @@ function tiny.update(world, dt, filter)
                 else
                     update(system, dt)
                 end
-                --local endTimeMs = playdate.getCurrentTimeMilliseconds()
-                --print(tostring(endTimeMs - currentMs) .. "ms taken to update " .. system.name)
+                if tinyLogSystemUpdateTime then
+                    local endTimeMs = getCurrentTimeMilliseconds()
+                    print(tostring(endTimeMs - currentMs) .. "ms taken to update system '" .. system.name .. "'")
+                end
             end
 
             system.modified = false
         end
     end
-    --print("")
+    if tinyLogSystemUpdateTime then
+        print("")
+    end
 
     -- Iterate through Systems IN ORDER AGAIN
     for i = 1, #systems do
diff --git a/src/main.lua b/src/main.lua
index 1e6dd2b..c32b07b 100644
--- a/src/main.lua
+++ b/src/main.lua
@@ -7,6 +7,7 @@ import("CoreLibs/timer.lua")
 import("CoreLibs/ui.lua")
 import("CoreLibs/utilities/where.lua")
 
+import("../lib/tiny-debug.lua")
 import("../lib/tiny.lua")
 
 local tiny <const> = tiny
diff --git a/src/systems/camera-pan.lua b/src/systems/camera-pan.lua
index 6f11c89..b9a2574 100644
--- a/src/systems/camera-pan.lua
+++ b/src/systems/camera-pan.lua
@@ -1,7 +1,5 @@
 local gfx <const> = playdate.graphics
 
-local focusPriority = {}
-
 Camera = {
     pan = {
         x = 0,
@@ -11,6 +9,8 @@ Camera = {
 
 expireBelowScreenSystem = filteredSystem("expireBelowScreen", { position = T.XyPair, expireBelowScreenBy = T.number })
 
+local focusPriority = {}
+
 cameraPanSystem = filteredSystem("cameraPan", { focusPriority = T.number, position = T.XyPair }, function(e, dt)
     if e.focusPriority >= focusPriority.priority then
         focusPriority.position = e.position
diff --git a/src/tiny-tools.lua b/src/tiny-tools.lua
index 106c379..26d6917 100644
--- a/src/tiny-tools.lua
+++ b/src/tiny-tools.lua
@@ -3,6 +3,10 @@
 ---@param process fun(entity: T, dt: number, system: System)
 ---@return System | { entities: T[] }
 function filteredSystem(name, shape, process)
+    assert(type(name) == "string")
+    assert(type(shape) == "table")
+    assert(process == nil or type(process) == "function")
+
     local system = tiny.processingSystem()
     system.name = name
     local keys = {}