diff --git a/README.md b/README.md
index f3e695f..f595f98 100644
--- a/README.md
+++ b/README.md
@@ -31,10 +31,65 @@ The file is a dart array of formulas. Each formula is a dart set literal
         },
         "d4rt_code": "F = m*a;"
         
+    },
+    {
+        "name": 'Test argument order',
+        "input": [
+          'z':{ "magnitude": 'scalar'},
+          'a':{ "magnitude": 'scalar'},
+          'y':{ "magnitude": 'scalar'},
+        ],
+        "output": { 'result', "magnitude": 'scalar' },
+        "d4rtCode": '''
+              result = a * 100 + y * 10 + z;
+          ''',
     }
 ]
 ```
 
+# Unit file description
+
+```dart
+[
+  {
+    "name": 'meter',
+    "symbol": 'm',
+    "isBase": true
+  },
+  {
+    "name": 'inch',
+    "symbol" 'in',
+    "baseUnit": 'meter',
+    "factor": 0.0254
+  },
+  {
+    "name": 'nautical mile',
+    "symbol": 'Nm',
+    "baseUnit": 'meter',
+    "factor": 1852
+  },
+  {
+    "name": 'Kelvin',
+    "symbol": "Kº",
+    "isBase": true,
+  },
+  {
+    "name": 'Celsius',
+    "symbol": "Cº",
+    "baseUnit" : "Kelvin",
+    "toBase": "x + 273.15",
+    "fromBase": "x - 273.15"
+  },
+  {
+    "name": 'Fahrenheit',
+    "symbol": "Fº",
+    "baseUnit" : "Kelvin",
+    "toBase": "(x - 32) × 5/9 + 273.15",
+    "fromBase": "x - 273.15) * 9/5 + 32"
+  }
+]
+```
+
 ## Features
 
 ### Formula Search and Computation
diff --git a/firejail-warp-terminal.profile b/firejail-warp-terminal.profile
index 89bd667..5406c7b 100644
--- a/firejail-warp-terminal.profile
+++ b/firejail-warp-terminal.profile
@@ -1,5 +1,5 @@
 # launch as: firejail --profile=firejail-warp-terminal.profile /opt/warpdotdev/warp-terminal/warp
-private /home/alvaro/repos/d4rt-formulas/
+private /home/alvaro/repos/d4rt_formulas/
 blacklist /datos-1T
 blacklist /datos-luks/
 blacklist /media
@@ -8,3 +8,4 @@ blacklist /media
 # noroot            # don't run as root
 caps.drop all     # drop Linux capabilities
 # seccomp           # enable syscall filtering
+First version of a formula widget
\ No newline at end of file
diff --git a/lib/corpus.dart b/lib/corpus.dart
new file mode 100644
index 0000000..0089404
--- /dev/null
+++ b/lib/corpus.dart
@@ -0,0 +1,96 @@
+import 'package:d4rt/d4rt.dart';
+import 'package:collection/collection.dart';
+import 'package:d4rt_formulas/d4rt_formulas.dart';
+
+class Multimap<K, V> extends DelegatingMap<K, List<V>> {
+  final Map<K, List<V>> _map;
+
+  Multimap(super.map) : _map = map;
+
+  factory Multimap.create() {
+    return Multimap({});
+  }
+
+  @override
+  List<V>? operator [](Object? key) {
+    if (_map.containsKey(key)) {
+      return super[key];
+    }
+    final List<V> newList = [];
+    super[key as K] = newList;
+    return super[key];
+  }
+}
+
+class UnitCorpus {
+  final Multimap<String, String> _baseToUnits = Multimap.create();
+  final Map<String, UnitSpec> _allUnits = {};
+
+  void loadUnits(List<UnitSpec> units, [bool replaceOnDuplicates = false]) {
+    for (final unit in units) {
+      if (!replaceOnDuplicates && _allUnits.containsKey(unit.name)) {
+        throw ArgumentError("Duplicate unit:${unit}");
+      }
+      _allUnits[unit.name] = unit;
+      _baseToUnits[unit.baseUnit]?.add(unit.name);
+    }
+  }
+
+  UnitSpec operator [](String unit) {
+    if (!_allUnits.containsKey(unit)) {
+      throw ArgumentError("Unit not found:${unit}");
+    }
+    return _allUnits.get(unit);
+  }
+
+  UnitSpec get(String unit) => this[unit];
+
+  String _converterFromCodeString(Number x, String codeString) {
+    final buffer = StringBuffer();
+    buffer.writeln("final x = ${x};");
+    buffer.writeln("main(){return $codeString;}");
+    final code = buffer.toString();
+    return code;
+  }
+
+  Number _convertToBase(Number x, String fromUnit) {
+    final unit = this[fromUnit];
+
+    if (unit.factorFromUnitToBase != null) {
+      return x * (unit.factorFromUnitToBase as Number);
+    }
+
+    if (unit.codeFromUnitToBase == null) {
+      throw ArgumentError("Unit has no codeFromUnitToBase: $unit");
+    }
+
+    final d4rt = D4rt();
+    final completeSource = _converterFromCodeString(x, unit.codeFromUnitToBase as String);
+    final ret = d4rt.execute(source: completeSource);
+    return ret as Number;
+  }
+
+  Number _convertFromBase(Number x, String toUnit) {
+    final unit = this[toUnit];
+
+    if (unit.factorFromUnitToBase != null) {
+      return x / (unit.factorFromUnitToBase as Number);
+    }
+
+    if (unit.codeFromBaseToUnit == null) {
+      throw ArgumentError("Unit has no codeFromBaseToUnit: $unit");
+    }
+
+    final d4rt = D4rt();
+    final completeSource = _converterFromCodeString(x, unit.codeFromBaseToUnit as String);
+    final ret = d4rt.execute(source: completeSource);
+    return ret as Number;
+  }
+
+  Number convert(Number x, String fromUnit, String toUnit) {
+    final xBase = _convertToBase(x, fromUnit);
+    final xTo = _convertFromBase(xBase, toUnit);
+
+    return xTo;
+  }
+}
diff --git a/lib/formula_models.dart b/lib/formula_models.dart
index bea9371..4788486 100644
--- a/lib/formula_models.dart
+++ b/lib/formula_models.dart
@@ -1,6 +1,106 @@
 import 'package:d4rt/d4rt.dart';
 import 'package:collection/collection.dart';
 
+abstract class SetUtils {
+  static Object safeGet(Map<Object?, Object?> map, String key) {
+    if (!map.containsKey(key)) {
+      throw ArgumentError("Key not found: $key -- $map");
+    }
+    return map[key] ?? "Not possible!!!";
+  }
+
+  static String stringValue(Map<Object?, Object?> map, String key) {
+    return safeGet(map, key).toString();
+  }
+
+  static List<Object?> listValue(Map<Object?, Object?> map, String key) {
+    return safeGet(map, key) as List<Object?>;
+  }
+
+  static Number numberValue(Map<Object?, Object?> map, String key) {
+    return double.parse(stringValue(map, key));
+  }
+}
+
+typedef Number = double;
+
+
+class UnitSpec {
+  final String name;
+  final String baseUnit;
+  final String symbol;
+  final Number? factorFromUnitToBase;
+  final String? codeFromUnitToBase;
+  final String? codeFromBaseToUnit;
+
+  static final BASEUNIT="BASEUNIT";
+
+  UnitSpec({
+    required this.name,
+    required this.baseUnit,
+    required this.symbol,
+    this.factorFromUnitToBase,
+    this.codeFromBaseToUnit,
+    this.codeFromUnitToBase,
+  });
+
+  factory UnitSpec.fromSet(Map<Object?, Object?> theSet) {
+    String name = SetUtils.stringValue(theSet, "name");
+    String symbol = SetUtils.stringValue(theSet, "symbol");
+
+    if( theSet.containsKey("isBase") ){
+      return UnitSpec(name: name, baseUnit: BASEUNIT, symbol: symbol, factorFromUnitToBase: 1);
+    }
+
+    String baseUnit = SetUtils.stringValue(theSet, "baseUnit");
+
+    if (theSet.containsKey("factor")) {
+      Number factorFromUnitToBase = SetUtils.numberValue(theSet, "factor");
+      return UnitSpec(
+        name: name,
+        baseUnit: baseUnit,
+        symbol: symbol,
+        factorFromUnitToBase: factorFromUnitToBase,
+      );
+    }
+    else if( theSet.containsKey("toBase")) {
+      String codeFromBaseToUnit = SetUtils.stringValue(
+        theSet,
+        "fromBase",
+      );
+      String codeFromUnitToBase = SetUtils.stringValue(
+        theSet,
+        "toBase",
+      );
+
+      return UnitSpec(name: name,
+          baseUnit: baseUnit,
+          symbol: symbol,
+          codeFromBaseToUnit: codeFromBaseToUnit,
+          codeFromUnitToBase: codeFromUnitToBase);
+    }
+    else{
+      throw ArgumentError( "Need factor or toBase/fromBase");
+    }
+
+
+  }
+
+  static List<UnitSpec> fromArrayStringLiteral(String arrayStringLiteral) {
+    var d4rt = D4rt();
+    final buffer = StringBuffer();
+    buffer.write("main(){ return $arrayStringLiteral; }");
+    final code = buffer.toString();
+
+    final List<Object?> list = d4rt.execute(source: code);
+
+    final units = list.map((set) => UnitSpec.fromSet(set as Map));
+
+    return units.toList(growable: false);
+  }
+
+}
+
 class VariableSpec {
   final String name;
   final String magnitude;
@@ -65,10 +165,10 @@ class Formula {
   List<String> inputVarNames() =>
       input.map((v) => v.name).toList(growable: false);
 
-  factory Formula.fromStringLiteral( String setStringLiteral ){
+  factory Formula.fromStringLiteral(String setStringLiteral) {
     var d4rt = D4rt();
     final buffer = StringBuffer();
-    buffer.write( "main(){ return $setStringLiteral; }");
+    buffer.write("main(){ return $setStringLiteral; }");
     final code = buffer.toString();
 
     final Map<Object?, Object?> setLiteral = d4rt.execute(source: code);
@@ -76,48 +176,34 @@ class Formula {
     return Formula.fromSet(setLiteral);
   }
 
-  static List<Formula> fromArrayStringLiteral( String arrayStringLiteral ){
+  static List<Formula> fromArrayStringLiteral(String arrayStringLiteral) {
     var d4rt = D4rt();
     final buffer = StringBuffer();
-    buffer.write( "main(){ return $arrayStringLiteral; }");
+    buffer.write("main(){ return $arrayStringLiteral; }");
     final code = buffer.toString();
 
     final List<Object?> list = d4rt.execute(source: code);
 
-    final formulas = list.map( (set) => Formula.fromSet(set as Map) );
+    final formulas = list.map((set) => Formula.fromSet(set as Map));
 
     return formulas.toList(growable: false);
   }
 
   factory Formula.fromSet(Map<Object?, Object?> theSet) {
-
-    Object safeGet(Map<Object?, Object?> map, String key){
-      if( !map.containsKey(key) ){
-        throw ArgumentError( "Key not found: $key -- $map" );
-      }
-      return map[key] ?? "Not possible!!!";
-    }
-
-    String stringValue(Map<Object?, Object?> map, String key){
-      return safeGet(map, key).toString();
-    }
-
-    List<Object?> listValue(Map<Object?, Object?> map, String key){
-      return safeGet(map,key) as List<Object?>;
-    }
-
     VariableSpec parseVar(Map<Object?, Object?> varSpec) {
-      String name = stringValue(varSpec, "name");
-      String magnitude = stringValue(varSpec, "magnitude");
+      String name = SetUtils.stringValue(varSpec, "name");
+      String magnitude = SetUtils.stringValue(varSpec, "magnitude");
       return VariableSpec(name: name, magnitude: magnitude);
     }
 
-    String name = stringValue( theSet, "name" );
-    final List<Object?> inputSet = listValue( theSet, "input");
-    List<VariableSpec> input = inputSet.map( (v) => parseVar(v as Map)).toList(growable: false);
+    String name = SetUtils.stringValue(theSet, "name");
+    final List<Object?> inputSet = SetUtils.listValue(theSet, "input");
+    List<VariableSpec> input = inputSet
+        .map((v) => parseVar(v as Map))
+        .toList(growable: false);
     Map<Object?, Object?> outputSet = theSet.get("output");
     VariableSpec output = parseVar(outputSet);
-    String d4rtCode = theSet.get("d4rtCode");
+    String d4rtCode = SetUtils.stringValue(theSet, "d4rtCode");
 
     return Formula(
       name: name,
diff --git a/lib/units/distance.d4rt.units b/lib/units/distance.d4rt.units
new file mode 100644
index 0000000..0e26a90
--- /dev/null
+++ b/lib/units/distance.d4rt.units
@@ -0,0 +1,41 @@
+[
+  {"name": "meter", "symbol": "m", "isBase": true},
+  {"name": "inch", "symbol": "in", "baseUnit": "meter", "factor" : 0.0254 },
+  {"name": "kilometer", "symbol": "km", "baseUnit": "meter", "factor": 1000},
+  {
+    "name": "nautical mile",
+    "symbol": "Nm",
+    "baseUnit": "meter",
+    "factor": 1852,
+  },
+  {
+    "name": "light-year",
+    "symbol": "ly",
+    "baseUnit": "meter",
+    "factor": 9.461e15,
+  },
+  {
+    "name": "astronomical unit",
+    "symbol": "AU",
+    "baseUnit": "meter",
+    "factor": 1.496e11,
+  },
+  {"name": "rod", "symbol": "rd", "baseUnit": "meter", "factor": 5.0292},
+  {"name": "chain", "symbol": "ch", "baseUnit": "meter", "factor": 20.1168},
+  {"name": "furlong", "symbol": "fur", "baseUnit": "meter", "factor": 201.168},
+  {"name": "league", "symbol": "lea", "baseUnit": "meter", "factor": 4828.032},
+  {"name": "elbow", "symbol": "elb", "baseUnit": "meter", "factor": 0.4572},
+  {"name": "hand", "symbol": "hh", "baseUnit": "meter", "factor": 0.1016},
+  {"name": "cubit", "symbol": "cub", "baseUnit": "meter", "factor": 0.4572},
+  {"name": "span", "symbol": "sp", "baseUnit": "meter", "factor": 0.2286},
+  {"name": "fathom", "symbol": "ftm", "baseUnit": "meter", "factor": 1.8288},
+  {"name": "finger", "symbol": "fng", "baseUnit": "meter", "factor": 0.0222},
+  {
+    "name": "Roman mile",
+    "symbol": "mil.rom",
+    "baseUnit": "meter",
+    "factor": 1479.5,
+  },
+  {"name": "Chinese li", "symbol": "li", "baseUnit": "meter", "factor": 500},
+  {"name": "Japanese ri", "symbol": "ri", "baseUnit": "meter", "factor": 3927}
+]
diff --git a/lib/units/temperature.d4rt.units b/lib/units/temperature.d4rt.units
new file mode 100644
index 0000000..84cf5e9
--- /dev/null
+++ b/lib/units/temperature.d4rt.units
@@ -0,0 +1,74 @@
+[
+  {"name": "Kelvin", "symbol": "K", "isBase": true},
+  {
+    "name": "Celsius",
+    "symbol": "°C",
+    "baseUnit": "Kelvin",
+    "toBase": "x + 273.15",
+    "fromBase": "x - 273.15",
+  },
+  {
+    "name": "Fahrenheit",
+    "symbol": "°F",
+    "baseUnit": "Kelvin",
+    "toBase": "(x - 32) * 5/9 + 273.15",
+    "fromBase": "(x - 273.15) * 9/5 + 32",
+  },
+  {
+    "name": "Rankine",
+    "symbol": "°R",
+    "baseUnit": "Kelvin",
+    "toBase": "x * 5/9",
+    "fromBase": "x * 9/5",
+  },
+  {
+    "name": "Réaumur",
+    "symbol": "°Ré",
+    "baseUnit": "Kelvin",
+    "toBase": "x * 5/4 + 273.15",
+    "fromBase": "(x - 273.15) * 4/5",
+  },
+  {
+    "name": "Delisle",
+    "symbol": "°D",
+    "baseUnit": "Kelvin",
+    "toBase": "373.15 - x * 2/3",
+    "fromBase": "(373.15 - x) * 3/2",
+  },
+  {
+    "name": "Rømer",
+    "symbol": "°Rø",
+    "baseUnit": "Kelvin",
+    "toBase": "(x - 7.5) * 40/21 + 273.15",
+    "fromBase": "(x - 273.15) * 21/40 + 7.5",
+  },
+  {
+    "name": "Gas Mark",
+    "symbol": "GM",
+    "baseUnit": "Kelvin",
+    "toBase": """
+      if (x < 1) {
+        double celsius = (243 - 25 * (log(1 / x) / log(2))) / 1.8;
+        return celsius + 273.15; // convert Celsius to Kelvin
+      } else {
+        double celsius = x * 14 + 121;
+        return celsius + 273.15;
+      }
+    """,
+    "fromBase": """
+      double celsius = x - 273.15; // convert Kelvin to Celsius
+      if (celsius < 135) { // corresponds to G < 1
+        return pow(2, (1.8 * celsius - 243) / 25);
+      } else {
+        return (celsius - 121) / 14;
+      }
+    """
+  },
+  {
+    "name": "Solar Temperature",
+    "symbol": "°Sol",
+    "baseUnit": "Kelvin",
+    "toBase": "x * 1000000",
+    "fromBase": "x / 1000000",
+  }
+]
diff --git a/pubspec.lock b/pubspec.lock
index 5bc3a6b..76ccc2a 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -66,7 +66,7 @@ packages:
     source: hosted
     version: "1.1.2"
   collection:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: collection
       sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
@@ -171,6 +171,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.1.3"
+  http:
+    dependency: transitive
+    description:
+      name: http
+      sha256: bb2ce4590bc2667c96f318d68cac1b5a7987ec819351d32b1c987239a815e007
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.5.0"
   http_multi_server:
     dependency: transitive
     description:
@@ -315,6 +323,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.2.0"
+  resource_portable:
+    dependency: "direct main"
+    description:
+      name: resource_portable
+      sha256: "8ffa33b0769645e26d82c8f4e79adde3dd34b9e0bba981166d4e3798f39cffd9"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.2"
   shelf:
     dependency: transitive
     description:
diff --git a/pubspec.yaml b/pubspec.yaml
index 34c42ec..67fff6c 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -34,6 +34,7 @@ dependencies:
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.
   cupertino_icons: ^1.0.8
+  resource_portable:
   d4rt:
   flutter_d4rt:
 
diff --git a/test/formula_models_test.dart b/test/formula_models_test.dart
index 2ee92f3..77af9e5 100644
--- a/test/formula_models_test.dart
+++ b/test/formula_models_test.dart
@@ -1,7 +1,11 @@
-
+import 'package:d4rt_formulas/corpus.dart';
 import 'package:d4rt_formulas/formula_evaluator.dart';
+import 'package:flutter/services.dart';
 import 'package:test/test.dart';
 import 'package:d4rt_formulas/formula_models.dart';
+import 'dart:convert' show utf8;
+
+import 'package:resource_portable/resource.dart' show Resource;
 
 void main() {
 
@@ -68,13 +72,13 @@ void main() {
     final setLiteral = {
       "name": "Newton's second law",
       "input": [
-        { "name": 'm', "magnitude": 'mass'},
-        { "name": 'a', "magnitude": 'acceleration'}
+        {"name": 'm', "magnitude": 'mass'},
+        {"name": 'a', "magnitude": 'acceleration'},
       ],
-      "output": { "name": 'F', "magnitude": 'force'},
+      "output": {"name": 'F', "magnitude": 'force'},
       "d4rtCode": '''
               F = a * m;
-          '''
+          ''',
     };
 
     final formula = Formula.fromSet(setLiteral);
@@ -88,7 +92,7 @@ void main() {
     expect(result, 98.0); // F = m * a = 10 * 9.8 = 98 N
   });
 
-  test( 'd4rt parses formula from literal', (){
+  test('d4rt parses formula from literal', () {
     final literal = """
     {
       "name": "Newton's second law",
@@ -112,11 +116,9 @@ void main() {
     });
 
     expect(result, 98.0); // F = m * a = 10 * 9.8 = 98 N
-
   });
 
-
-  test( 'd4rt parses formula from list literal', (){
+  test('d4rt parses formula from list literal', () {
     final literal = """
     [
     {
@@ -155,8 +157,5 @@ void main() {
     });
 
     expect(result, 98.0); // F = m * a = 10 * 9.8 = 98 N
-
   });
-
 }
-