diff --git a/app/Services/RuleEngineService.php b/app/Services/RuleEngineService.php
index 2b912dc..8a04378 100644
--- a/app/Services/RuleEngineService.php
+++ b/app/Services/RuleEngineService.php
@@ -181,6 +181,15 @@ class RuleEngineService
             $testSiteID = is_numeric($order['TestSiteID']) ? (int) $order['TestSiteID'] : null;
         }
 
+        $testCode = $action['testCode'] ?? null;
+        if ($testCode !== null) {
+            $resolvedId = $this->resolveTestSiteIdByCode($testCode);
+            if ($resolvedId === null) {
+                throw new \Exception('SET_RESULT unknown test code: ' . $testCode);
+            }
+            $testSiteID = $resolvedId;
+        }
+
         if ($testSiteID === null) {
             throw new \Exception('SET_RESULT requires testSiteID');
         }
@@ -192,6 +201,8 @@ class RuleEngineService
             $value = $action['value'] ?? null;
         }
 
+        $testSiteCode = $testCode ?? $this->resolveTestSiteCode($testSiteID);
+
         $db = \Config\Database::connect();
 
         // Check if patres row exists
@@ -214,7 +225,7 @@ class RuleEngineService
             $ok = $db->table('patres')->insert([
                 'OrderID' => $internalOID,
                 'TestSiteID' => $testSiteID,
-                'TestSiteCode' => $this->resolveTestSiteCode($testSiteID),
+                'TestSiteCode' => $testSiteCode,
                 'Result' => $value,
                 'CreateDate' => date('Y-m-d H:i:s'),
             ]);
@@ -360,4 +371,19 @@ class RuleEngineService
             return null;
         }
     }
+
+    private function resolveTestSiteIdByCode(string $testSiteCode): ?int
+    {
+        try {
+            $testDefSiteModel = new TestDefSiteModel();
+            $row = $testDefSiteModel->where('TestSiteCode', $testSiteCode)->where('EndDate', null)->first();
+            if (empty($row['TestSiteID'])) {
+                return null;
+            }
+
+            return (int) $row['TestSiteID'];
+        } catch (\Throwable $e) {
+            return null;
+        }
+    }
 }
diff --git a/app/Services/RuleExpressionService.php b/app/Services/RuleExpressionService.php
index 11bdba1..3d7c4bf 100644
--- a/app/Services/RuleExpressionService.php
+++ b/app/Services/RuleExpressionService.php
@@ -53,7 +53,8 @@ class RuleExpressionService
      * - priority('R'|'S'|'U') -> order["Priority"] == 'S'
      * - age > 18 -> age > 18
      * - requested('CODE') -> requested('CODE') (resolved at runtime)
-     * - result_set(value)
+     * - result_set('TestSiteCode', value)
+     * - result_set(value) (deprecated, uses current context TestSiteID)
      * - test_insert('CODE')
      * - test_delete('CODE')
      * - comment_insert('text')
@@ -242,9 +243,22 @@ class RuleExpressionService
             ];
         }
 
-        // result_set(value) [aliases: set_result]
-        if (preg_match('/^(result_set|set_result)\s*\(\s*(.+?)\s*\)$/is', $action, $m)) {
-            $value = trim($m[2]);
+        // result_set(value) or result_set('CODE', value) [aliases: set_result]
+        if (preg_match('/^(result_set|set_result)\s*\(\s*(.+)\s*\)$/is', $action, $m)) {
+            $args = $this->splitTopLevel($m[2], ',', 2);
+            if (empty($args)) {
+                throw new \InvalidArgumentException('result_set requires a value expression');
+            }
+
+            $testCode = null;
+            if (count($args) === 2) {
+                $testCode = $this->unquoteStringArgument($args[0]);
+                if ($testCode === null) {
+                    throw new \InvalidArgumentException('result_set test code must be a quoted string');
+                }
+            }
+
+            $value = trim($args[count($args) - 1]);
 
             // Check if it's a number
             if (is_numeric($value)) {
@@ -252,6 +266,7 @@ class RuleExpressionService
                     'type' => 'RESULT_SET',
                     'value' => strpos($value, '.') !== false ? (float) $value : (int) $value,
                     'valueExpr' => $value,
+                    'testCode' => $testCode,
                 ];
             }
 
@@ -261,6 +276,7 @@ class RuleExpressionService
                     'type' => 'RESULT_SET',
                     'value' => $vm[1],
                     'valueExpr' => '"' . addslashes($vm[1]) . '"',
+                    'testCode' => $testCode,
                 ];
             }
 
@@ -268,6 +284,7 @@ class RuleExpressionService
             return [
                 'type' => 'RESULT_SET',
                 'valueExpr' => $value,
+                'testCode' => $testCode,
             ];
         }
 
@@ -666,4 +683,24 @@ class RuleExpressionService
             'endIndex' => $start + 2,
         ];
     }
+
+    private function unquoteStringArgument(string $value): ?string
+    {
+        $value = trim($value);
+        if ($value === '') {
+            return null;
+        }
+
+        $quote = $value[0];
+        if ($quote !== '"' && $quote !== "'") {
+            return null;
+        }
+
+        if (substr($value, -1) !== $quote) {
+            return null;
+        }
+
+        $content = substr($value, 1, -1);
+        return stripcslashes($content);
+    }
 }
diff --git a/docs/calculator-operators.md b/docs/calculator-operators.md
new file mode 100644
index 0000000..1e289af
--- /dev/null
+++ b/docs/calculator-operators.md
@@ -0,0 +1,309 @@
+# Calculator Service Operators Reference
+
+## Overview
+
+The `CalculatorService` (`app/Services/CalculatorService.php`) uses the [mossadal/math-parser](https://github.com/mossadal/math-parser) library to safely evaluate mathematical expressions. This document lists all available operators, functions, and constants.
+
+---
+
+## Supported Operators
+
+### Arithmetic Operators
+
+| Operator | Description | Example | Result |
+|----------|-------------|---------|--------|
+| `+` | Addition | `5 + 3` | `8` |
+| `-` | Subtraction | `10 - 4` | `6` |
+| `*` | Multiplication | `6 * 7` | `42` |
+| `/` | Division | `20 / 4` | `5` |
+| `^` | Exponentiation (power) | `2 ^ 3` | `8` |
+| `!` | Factorial | `5!` | `120` |
+| `!!` | Semi-factorial (double factorial) | `5!!` | `15` |
+
+### Parentheses
+
+Use parentheses to control operation precedence:
+
+```
+(2 + 3) * 4   // Result: 20
+2 + 3 * 4     // Result: 14
+```
+
+---
+
+## Mathematical Functions
+
+### Rounding Functions
+
+| Function | Description | Example |
+|----------|-------------|---------|
+| `sqrt(x)` | Square root | `sqrt(16)` → `4` |
+| `round(x)` | Round to nearest integer | `round(3.7)` → `4` |
+| `ceil(x)` | Round up to integer | `ceil(3.2)` → `4` |
+| `floor(x)` | Round down to integer | `floor(3.9)` → `3` |
+| `abs(x)` | Absolute value | `abs(-5)` → `5` |
+| `sgn(x)` | Sign function | `sgn(-10)` → `-1` |
+
+### Trigonometric Functions (Radians)
+
+| Function | Description | Example |
+|----------|-------------|---------|
+| `sin(x)` | Sine | `sin(pi/2)` → `1` |
+| `cos(x)` | Cosine | `cos(0)` → `1` |
+| `tan(x)` | Tangent | `tan(pi/4)` → `1` |
+| `cot(x)` | Cotangent | `cot(pi/4)` → `1` |
+
+### Trigonometric Functions (Degrees)
+
+| Function | Description | Example |
+|----------|-------------|---------|
+| `sind(x)` | Sine (degrees) | `sind(90)` → `1` |
+| `cosd(x)` | Cosine (degrees) | `cosd(0)` → `1` |
+| `tand(x)` | Tangent (degrees) | `tand(45)` → `1` |
+| `cotd(x)` | Cotangent (degrees) | `cotd(45)` → `1` |
+
+### Hyperbolic Functions
+
+| Function | Description | Example |
+|----------|-------------|---------|
+| `sinh(x)` | Hyperbolic sine | `sinh(1)` → `1.175...` |
+| `cosh(x)` | Hyperbolic cosine | `cosh(1)` → `1.543...` |
+| `tanh(x)` | Hyperbolic tangent | `tanh(1)` → `0.761...` |
+| `coth(x)` | Hyperbolic cotangent | `coth(2)` → `1.037...` |
+
+### Inverse Trigonometric Functions
+
+| Function | Aliases | Description | Example |
+|----------|---------|-------------|---------|
+| `arcsin(x)` | `asin(x)` | Inverse sine | `arcsin(0.5)` → `0.523...` |
+| `arccos(x)` | `acos(x)` | Inverse cosine | `arccos(0.5)` → `1.047...` |
+| `arctan(x)` | `atan(x)` | Inverse tangent | `arctan(1)` → `0.785...` |
+| `arccot(x)` | `acot(x)` | Inverse cotangent | `arccot(1)` → `0.785...` |
+
+### Inverse Hyperbolic Functions
+
+| Function | Aliases | Description | Example |
+|----------|---------|-------------|---------|
+| `arsinh(x)` | `asinh(x)`, `arcsinh(x)` | Inverse hyperbolic sine | `arsinh(1)` → `0.881...` |
+| `arcosh(x)` | `acosh(x)`, `arccosh(x)` | Inverse hyperbolic cosine | `arcosh(2)` → `1.316...` |
+| `artanh(x)` | `atanh(x)`, `arctanh(x)` | Inverse hyperbolic tangent | `artanh(0.5)` → `0.549...` |
+| `arcoth(x)` | `acoth(x)`, `arccoth(x)` | Inverse hyperbolic cotangent | `arcoth(2)` → `0.549...` |
+
+### Logarithmic & Exponential Functions
+
+| Function | Aliases | Description | Example |
+|----------|---------|-------------|---------|
+| `exp(x)` | - | Exponential (e^x) | `exp(2)` → `7.389...` |
+| `log(x)` | `ln(x)` | Natural logarithm (base e) | `log(e)` → `1` |
+| `log10(x)` | `lg(x)` | Logarithm base 10 | `log10(100)` → `2` |
+
+---
+
+## Constants
+
+| Constant | Value | Description | Example |
+|----------|-------|-------------|---------|
+| `pi` | 3.14159265... | Ratio of circle circumference to diameter | `pi * r ^ 2` |
+| `e` | 2.71828182... | Euler's number | `e ^ x` |
+| `NAN` | Not a Number | Invalid mathematical result | - |
+| `INF` | Infinity | Positive infinity | - |
+
+---
+
+## Variables in CalculatorService
+
+When using `calculateFromDefinition()`, the following variables are automatically available:
+
+| Variable | Description | Type |
+|----------|-------------|------|
+| `{result}` | The test result value | Float |
+| `{factor}` | Calculation factor (default: 1) | Float |
+| `{gender}` | Gender value (0=Unknown, 1=Female, 2=Male) | Integer |
+| `{age}` | Patient age | Float |
+| `{ref_low}` | Reference range low value | Float |
+| `{ref_high}` | Reference range high value | Float |
+
+### Gender Mapping
+
+The `gender` variable accepts the following values:
+
+| Value | Description |
+|-------|-------------|
+| `0` | Unknown |
+| `1` | Female |
+| `2` | Male |
+
+Or use string values: `'unknown'`, `'female'`, `'male'`
+
+---
+
+## Implicit Multiplication
+
+The parser supports implicit multiplication (no explicit `*` operator needed):
+
+| Expression | Parsed As | Result (x=2, y=3) |
+|------------|-----------|-------------------|
+| `2x` | `2 * x` | `4` |
+| `x sin(x)` | `x * sin(x)` | `1.818...` |
+| `2xy` | `2 * x * y` | `12` |
+| `x^2y` | `x^2 * y` | `12` |
+
+**Note:** Implicit multiplication has the same precedence as explicit multiplication. `xy^2z` is parsed as `x*y^2*z`, NOT as `x*y^(2*z)`.
+
+---
+
+## Usage Examples
+
+### Basic Calculation
+
+```php
+use App\Services\CalculatorService;
+
+$calculator = new CalculatorService();
+
+// Simple arithmetic
+$result = $calculator->calculate("5 + 3 * 2");
+// Result: 11
+
+// Using functions
+$result = $calculator->calculate("sqrt(16) + abs(-5)");
+// Result: 9
+
+// Using constants
+$result = $calculator->calculate("2 * pi * r", ['r' => 5]);
+// Result: 31.415...
+```
+
+### With Variables
+
+```php
+$formula = "{result} * {factor} + 10";
+$variables = [
+    'result' => 5.2,
+    'factor' => 2
+];
+
+$result = $calculator->calculate($formula, $variables);
+// Result: 20.4
+```
+
+### BMI Calculation
+
+```php
+$formula = "{weight} / ({height} ^ 2)";
+$variables = [
+    'weight' => 70,   // kg
+    'height' => 1.75  // meters
+];
+
+$result = $calculator->calculate($formula, $variables);
+// Result: 22.86
+```
+
+### Gender-Based Calculation
+
+```php
+// Apply different multipliers based on gender
+$formula = "{result} * (1 + 0.1 * {gender})";
+$variables = [
+    'result' => 100,
+    'gender' => 1  // Female = 1
+];
+
+$result = $calculator->calculate($formula, $variables);
+// Result: 110
+```
+
+### Complex Formula
+
+```php
+// Pythagorean theorem with rounding
+$formula = "round(sqrt({a} ^ 2 + {b} ^ 2))";
+$variables = [
+    'a' => 3,
+    'b' => 4
+];
+
+$result = $calculator->calculate($formula, $variables);
+// Result: 5
+```
+
+### Using calculateFromDefinition
+
+```php
+$calcDef = [
+    'FormulaCode' => '{result} * {factor} + {gender}',
+    'Factor' => 2
+];
+
+$testValues = [
+    'result' => 10,
+    'gender' => 1  // Female
+];
+
+$result = $calculator->calculateFromDefinition($calcDef, $testValues);
+// Result: 21 (10 * 2 + 1)
+```
+
+---
+
+## Formula Validation
+
+Validate formulas before storing them:
+
+```php
+$validation = $calculator->validate("{result} / {factor}");
+// Returns: ['valid' => true, 'error' => null]
+
+$validation = $calculator->validate("{result} /");
+// Returns: ['valid' => false, 'error' => 'Error message']
+```
+
+### Extract Variables
+
+Get a list of variables used in a formula:
+
+```php
+$variables = $calculator->extractVariables("{result} * {factor} + {age}");
+// Returns: ['result', 'factor', 'age']
+```
+
+---
+
+## Error Handling
+
+The service throws exceptions for invalid formulas or missing variables:
+
+```php
+try {
+    $result = $calculator->calculate("{result} / 0");
+} catch (\Exception $e) {
+    // Handle division by zero or other errors
+    log_message('error', $e->getMessage());
+}
+```
+
+Common errors:
+
+- **Invalid formula syntax**: Malformed expressions
+- **Missing variable**: Variable placeholder not provided in data array
+- **Non-numeric value**: Variables must be numeric
+- **Division by zero**: Mathematical error
+
+---
+
+## Best Practices
+
+1. **Always validate formulas** before storing in database
+2. **Use placeholder syntax** `{variable_name}` for clarity
+3. **Handle exceptions** in production code
+4. **Test edge cases** like zero values and boundary conditions
+5. **Document formulas** with comments in your code
+
+---
+
+## References
+
+- [math-parser GitHub](https://github.com/mossadal/math-parser)
+- [math-parser Documentation](http://mossadal.github.io/math-parser/)
+- `app/Services/CalculatorService.php`
diff --git a/docs/test-rule-engine.md b/docs/test-rule-engine.md
index f3e6d18..074d37a 100644
--- a/docs/test-rule-engine.md
+++ b/docs/test-rule-engine.md
@@ -90,7 +90,8 @@ Each rule compiles and runs independently when its trigger fires and the test is
 
 | Action | Description | Example |
 |--------|-------------|---------|
-| `result_set(value)` | Write to `patres.Result` for the current order/test using the provided value | `result_set(0.5)` |
+| `result_set(value)` | (deprecated) Write to `patres.Result` for the current context test | `result_set(0.5)` |
+| `result_set('CODE', value)` | Target a specific test by `TestSiteCode`, allowing multiple tests to be updated in one rule | `result_set('tesA', 0.5)` |
 | `test_insert('CODE')` | Insert a test row by `TestSiteCode` if it doesn’t already exist for the order | `test_insert('HBA1C')` |
 | `test_delete('CODE')` | Remove a previously requested test from the current order when the rule deems it unnecessary | `test_delete('INS')` |
 | `comment_insert('text')` | Insert an order comment (`ordercom`) describing priority or clinical guidance | `comment_insert('Male patient - review')` |
@@ -102,15 +103,15 @@ Each rule compiles and runs independently when its trigger fires and the test is
 
 1. **Compiled expression required:** Rules without `ConditionExprCompiled` are ignored (see `RuleEngineService::run`).
 2. **Order context:** `context.order.InternalOID` must exist for any action that writes to `patres` or `ordercom`.
-3. **TestSiteID:** `result_set()` needs `testSiteID` (either provided in context or from `order.TestSiteID`). `test_insert()` resolves a `TestSiteID` via the `TestSiteCode` in `TestDefSiteModel`, and `test_delete()` removes the matching `TestSiteID` rows when needed.
+3. **TestSiteID:** `result_set()` needs `testSiteID` (either provided in context or from `order.TestSiteID`). When you provide a `TestSiteCode` as the first argument (`result_set('tesA', value)`), the engine resolves that code before writing the result. `test_insert()` resolves a `TestSiteID` via the `TestSiteCode` in `TestDefSiteModel`, and `test_delete()` removes the matching `TestSiteID` rows when needed.
 4. **Requested check:** `requested('CODE')` inspects `patres` rows for the same `OrderID` and `TestSiteCode`.
 
 ## Examples
 
 ```
-if(sex('M'); result_set(0.5); result_set(0.6))
+if(sex('M'); result_set('tesA', 0.5):result_set('tesB', 1.2); result_set('tesA', 0.6):result_set('tesB', 1.0))
 ```
-Returns `0.5` for males, `0.6` otherwise.
+Sets both `tesA`/`tesB` results together per branch.
 
 ```
 if(requested('GLU'); test_insert('HBA1C'):test_insert('INS'); nothing)
diff --git a/issues.md b/issues.md
deleted file mode 100644
index 64de5ab..0000000
--- a/issues.md
+++ /dev/null
@@ -1 +0,0 @@
-[ ] account initial must be unique