diff --git a/README.md b/README.md
index 99f4c6b..b391f28 100644
--- a/README.md
+++ b/README.md
@@ -23,3 +23,15 @@ $ yarn circuit
 $ npx hardhat node --fork <https://eth-mainnet.alchemyapi.io/v2/API_KEY> --fork-block-number 11827889
 $ npx hardhat test
 ```
+
+## Checklist for batch size changing
+
+find and replace the `CHUNK_TREE_HEIGHT = ` in following files
+
+1. `circuits/BatchTreeUpdate.circom`
+2. `contracts/TornadoTrees.sol`
+3. `tornadoTrees.test.js`
+
+## build large circuits
+
+1. docker build . -t tornadocash/tornado-trees
diff --git a/circuits/BatchTreeUpdate.circom b/circuits/BatchTreeUpdate.circom
index e12f162..dd17ecd 100644
--- a/circuits/BatchTreeUpdate.circom
+++ b/circuits/BatchTreeUpdate.circom
@@ -74,20 +74,18 @@ template BatchTreeUpdate(levels, batchLevels, zeroBatchLeaf) {
 
 // zeroLeaf = keccak256("tornado") % FIELD_SIZE
 // zeroBatchLeaf is poseidon(zeroLeaf, zeroLeaf) (batchLevels - 1) times
-component main = BatchTreeUpdate(20, 2, 21572503925325825116380792768937986743990254033176521064707045559165336555197)
+function nthZero(n) {
+    if (n == 0) return 21663839004416932945382355908790599225266501822907911457504978515578255421292;
+    if (n == 1) return 11850551329423159860688778991827824730037759162201783566284850822760196767874;
+    if (n == 2) return 21572503925325825116380792768937986743990254033176521064707045559165336555197;
+    if (n == 3) return 11224495635916644180335675565949106569141882748352237685396337327907709534945;
+    if (n == 4) return 2399242030534463392142674970266584742013168677609861039634639961298697064915;
+    if (n == 5) return 13182067204896548373877843501261957052850428877096289097123906067079378150834;
+    if (n == 6) return 7106632500398372645836762576259242192202230138343760620842346283595225511823;
+    if (n == 7) return 17857585024203959071818533000506593455576509792639288560876436361491747801924;
+    if (n == 8) return 17278668323652664881420209773995988768195998574629614593395162463145689805534;
+    if (n == 9) return 209436188287252095316293336871467217491997565239632454977424802439169726471;
+}
 
-// for mainnet use 20, 7, 17278668323652664881420209773995988768195998574629614593395162463145689805534
-
-/*
-zeros of n-th order:
-21663839004416932945382355908790599225266501822907911457504978515578255421292
-11850551329423159860688778991827824730037759162201783566284850822760196767874
-21572503925325825116380792768937986743990254033176521064707045559165336555197
-11224495635916644180335675565949106569141882748352237685396337327907709534945
- 2399242030534463392142674970266584742013168677609861039634639961298697064915
-13182067204896548373877843501261957052850428877096289097123906067079378150834
- 7106632500398372645836762576259242192202230138343760620842346283595225511823
-17278668323652664881420209773995988768195998574629614593395162463145689805534
-  209436188287252095316293336871467217491997565239632454977424802439169726471
- 6509061943359659796226067852175931816441223836265895622135845733346450111408
-*/
+var CHUNK_TREE_HEIGHT = 2
+component main = BatchTreeUpdate(20, CHUNK_TREE_HEIGHT, nthZero(CHUNK_TREE_HEIGHT))