diff --git a/src/spring.luau b/src/spring.luau
index e60e3ae..024da91 100644
--- a/src/spring.luau
+++ b/src/spring.luau
@@ -200,7 +200,7 @@ local function spring<T>(source: () -> T, period: number?, damping_ratio: number
     return function()
         track(output)
         return output.cache
-    end
+    end, data
 end
 
 local function step_springs(dt: number)
@@ -224,6 +224,9 @@ local function step_springs(dt: number)
         local ff_123 = u_123*-c
         local ff_456 = u_456*-c
 
+
+        --assert(math.abs(fs_123.X) >= (math.abs(ff_123.X)), "damping exceeds restoring")
+
         -- calculate acceleration step
         local dv_123 = (fs_123 + ff_123)*dt
         local dv_456 = (fs_456 + ff_456)*dt
diff --git a/test/spring-test.luau b/test/spring-test.luau
index c22d955..233c91c 100644
--- a/test/spring-test.luau
+++ b/test/spring-test.luau
@@ -40,7 +40,7 @@ local function main()
     local effect = vide.effect
 
     local value = source(MAX)
-    local sprung = spring(value, 1, 0.3)
+    local sprung, data = (spring :: any)(value, 1, 19.16)
 
     effect(function()
         local v = sprung()
@@ -48,14 +48,15 @@ local function main()
         local reset = "\27[H\27[2J" -- ANSI clear terminal
         local offset = string.rep("\n", MAX - fv + OFFSET)
         local bar = testkit.color.gray(remainder_to_block(v - fv) .. "\n" .. string.rep(BLOCK .. "\n", fv))
-        print(reset .. offset .. bar)
+        local num = "\n" .. v
+        print(reset .. offset .. bar .. num)
     end)
-
-    local elapsed = 0
+    
+    local T = 1.5
+    local elapsed = T/2
     repeat local dt = step()
         vide.step(dt)
 
-        local T = 3
         elapsed += dt
         while elapsed >= T do
             elapsed -= T