diff --git a/TODO.md b/TODO.md
index e2b59b8c..8d825d0f 100644
--- a/TODO.md
+++ b/TODO.md
@@ -47,7 +47,6 @@
 ## ideas
 
 - generarion of 'platform.yml' by `heta init`
-- use the syntax 1//3 for rational numbers
 - deprecated `include` statement
 - `#move`, `#moveNS`
 - `#deleteNS` action
diff --git a/package.json b/package.json
index 83dc3239..f842e471 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "Programming platform for Quantitative Systems Pharmacology modeling in NodeJS",
   "main": "src/index.js",
   "scripts": {
-    "test:dev": "mocha test/module-system --config=./test/.mocharc.json",
+    "test:dev": "mocha test/check-units/calc-unit --config=./test/.mocharc.json",
     "test": "mocha test --config=./test/.mocharc.json",
     "jsdoc": "jsdoc -r -c .jsdoc.json --readme api-references.md -d docs/dev src",
     "test:cov": "nyc --reporter=lcov npm run test",
diff --git a/src/core/math-calc-unit.js b/src/core/math-calc-unit.js
index fa9bc074..87d4d1ce 100644
--- a/src/core/math-calc-unit.js
+++ b/src/core/math-calc-unit.js
@@ -63,11 +63,15 @@ function _calcUnit(_this, record){
         logger.warn(`Units inconsistency for "${record.index}" for logical operators here"${_this.toString()}", some of them is not dimensionless : "${argUnit}"`);
       }
       return new Unit();
-    } else if (_this.fn === 'pow') {
-      if (_this.args[1].type === 'ConstantNode') { // pow(x, 3)
-        let n = _this.args[1].value;
-        return argUnit[0].power(n);
-      } else { // pow(x, y)
+    } else if (_this.fn === 'pow') { // ^
+      let pArg = _this.args[1];
+      if (pArg.type === 'ConstantNode') { // x ^ 3
+        return argUnit[0].power(pArg.value);
+      } else if (pArg.type === 'ParenthesisNode' && pArg.content?.fn === 'divide' && pArg.content.args[0]?.type === 'ConstantNode' && pArg.content.args[1]?.type === 'ConstantNode') { // x ^ (1/2)
+        let numerator = pArg.content.args[0].value;
+        let denominator = pArg.content.args[1].value;
+        return argUnit[0].power(numerator).root(denominator);
+      } else { // x ^ y
         if (!argUnitDimensionless[0] || !argUnitDimensionless[1]) {
           let unitExpr = argUnit[0].toString() + '^' + argUnit[1].toString();
           logger.warn(`Units inconsistency for "${record.index}": power arguments must be dimensionless or second argument should be a number: "${_this.toString()}" : "${unitExpr}"`);
@@ -122,11 +126,15 @@ function _calcUnit(_this, record){
     } else if (_this.fn.name === 'cube') { // cube()
       return argUnit[0].power(3);
     } else if (_this.fn.name === 'sqrt') { // sqrt()
-      return argUnit[0].power(0.5);
+      return argUnit[0].root(2);
     } else if (_this.fn.name === 'pow') { // pow()
-      if (_this.args[1].type === 'ConstantNode') { // pow(x, 2)
-        let n = _this.args[1].value;
-        return argUnit[0].power(n);
+      let pArg = _this.args[1];
+      if (pArg.type === 'ConstantNode') { // pow(x, 2)
+        return argUnit[0].power(pArg.value);
+      } else if (pArg.fn === 'divide' && pArg.args[0]?.type === 'ConstantNode' && pArg.args[1]?.type === 'ConstantNode') { // pow(x, 1/2)
+        let numerator = pArg.args[0].value;
+        let denominator = pArg.args[1].value;
+        return argUnit[0].power(numerator).root(denominator);
       } else { // pow(x, y)
         if (!argUnitDimensionless[0] || !argUnitDimensionless[1]) {
           let unitExpr = argUnit[0].toString() + '^' + argUnit[1].toString();
@@ -136,11 +144,11 @@ function _calcUnit(_this, record){
         return argUnit[0];
       }
     } else if (_this.fn.name === 'nthRoot' && _this.args.length === 1) { // nthRoot()
-      return argUnit[0].power(0.5);
+      return argUnit[0].root(2);
     } else if (_this.fn.name === 'nthRoot') {
       if (_this.args[1].type === 'ConstantNode') { // nthRoot(x, 3)
         let n = _this.args[1].value;
-        return argUnit[0].power(1/n);
+        return argUnit[0].root(n);
       } else { // nthRoot(x, y)
         if (!argUnitDimensionless[0] || !argUnitDimensionless[1]) {
           let unitExpr = argUnit[0].toString() + '^' + argUnit[1].toString();
diff --git a/src/core/unit.js b/src/core/unit.js
index a453c694..dd4825fc 100644
--- a/src/core/unit.js
+++ b/src/core/unit.js
@@ -150,7 +150,14 @@ class Unit extends Array {
     if (typeof n !== 'number') throw new TypeError('n in power must be a Number, got' + n);
 
     return this.map((item) => {
-      return Object.assign({}, item, {exponent: n * item.exponent});
+      return Object.assign({}, item, {exponent: item.exponent * n});
+    });
+  }
+  root(n = 1) {
+    if (typeof n !== 'number') throw new TypeError('n in power must be a Number, got' + n);
+
+    return this.map((item) => {
+      return Object.assign({}, item, {exponent: item.exponent / n});
     });
   }
   /**
diff --git a/test/check-units/calc-unit.js b/test/check-units/calc-unit.js
index c7eb97d3..374ab941 100644
--- a/test/check-units/calc-unit.js
+++ b/test/check-units/calc-unit.js
@@ -34,6 +34,10 @@ let qArr = [
   {id: 'y12', class: 'Record', assignments: {start_: 'piecewise(k3, x1 >= k2, k2)'}},
   {id: 'y13', class: 'Record', assignments: {start_: 'piecewise(k3, x1 >= k2)'}},
   {id: 'y14', class: 'Record', assignments: {start_: 'piecewise(1, x1 >= k2, 2, x1 >= 2*k2, 0)'}},
+  // fraction in power
+  {id: 'x6', class: 'Record', units: 'metre^3', assignments: {start_: '1'}},
+  {id: 'y15', class: 'Record', assignments: {start_: 'x6^(2/3)'}},
+  {id: 'y16', class: 'Record', assignments: {start_: 'pow(x6, 2/3)'}},
 ];
 
 describe('Testing checkUnits() for components', () => {
@@ -200,6 +204,20 @@ describe('Testing checkUnits() for components', () => {
     expect(unit).to.be.equal('dimensionless');
   });
 
+  it('pow with fractions x^(1/2)', () => {
+    let y15 = p.namespaceStorage.get('nameless').get('y15');
+    let expr = y15.assignments.start_;
+    let unit = expr.calcUnit(y15).toString();
+    expect(unit).to.be.equal('metre^2');
+  });
+  
+  it('pow with fractions pow(x , 1/2)', () => {
+    let y16 = p.namespaceStorage.get('nameless').get('y16');
+    let expr = y16.assignments.start_;
+    let unit = expr.calcUnit(y16).toString();
+    expect(unit).to.be.equal('metre^2');
+  });
+
   it('No warnings', () => {
     let warnings = p.defaultLogs.filter(x=>x.level==='warn');
     //console.log(p.defaultLogs)