diff --git a/src/core/Value.d.ts b/src/core/Value.d.ts
index 3d3f938..c0c77a0 100644
--- a/src/core/Value.d.ts
+++ b/src/core/Value.d.ts
@@ -6,6 +6,6 @@ export interface Value {
   value: number;
   /** */
   precision?: number;
-  /**A string or text indicating the unit of measurement. The unit could be validated in the input form based on the UN/CEFACT Common Code list */
+  /** A string or text indicating the unit of measurement. The unit could be validated in the input form based on the UN/CEFACT Common Code list */
   units?: string;
 }
diff --git a/src/measurements/common/MeasurementVariable.d.ts b/src/measurements/common/MeasurementVariable.d.ts
index fb383fa..dcdfa81 100644
--- a/src/measurements/common/MeasurementVariable.d.ts
+++ b/src/measurements/common/MeasurementVariable.d.ts
@@ -17,13 +17,11 @@ export interface MeasurementVariable<
    *@TJS-examples ["absolute pressure"]
    */
   label: string;
-  /**
-   *
-   */
+  /** Scale representation of variable */
+  scale?: 'linear' | 'log'
+  /** Is not the independent variable */
   isDependent?: boolean;
-  /**
-   * An array containing numerical data
-   */
+  /** An array containing numerical data */
   data: DataType;
   /** One letter that allows to define the variable */
   symbol?: OneLetter;
@@ -33,4 +31,6 @@ export interface MeasurementVariable<
   max?: number;
   /** If defined indicates (true or false) if the data series is monotone  */
   isMonotone?: boolean;
+  /** This variable doesn't change with the dependent variable */
+  isConstant?: boolean;
 }
diff --git a/todo/general/CalculationLimits.d.ts b/todo/general/CalculationLimits.d.ts
new file mode 100644
index 0000000..02fae02
--- /dev/null
+++ b/todo/general/CalculationLimits.d.ts
@@ -0,0 +1,8 @@
+import { ValueXY } from './ValueXY';
+
+export interface CalculationLimits {
+  from: ValueXY;
+  to: ValueXY;
+}
+
+
diff --git a/todo/general/Integral.d.ts b/todo/general/Integral.d.ts
new file mode 100644
index 0000000..d745cd3
--- /dev/null
+++ b/todo/general/Integral.d.ts
@@ -0,0 +1,4 @@
+import { Value } from "../../src";
+import { CalculationLimits } from "./CalculationLimits";
+
+export type Integral = CalculationLimits & Value;
diff --git a/todo/general/Slope.d.ts b/todo/general/Slope.d.ts
new file mode 100644
index 0000000..48ccc49
--- /dev/null
+++ b/todo/general/Slope.d.ts
@@ -0,0 +1,15 @@
+// import type { RegressionScore } from 'ml-regression-base';
+import { CalculationLimits } from "./CalculationLimits";
+
+interface RegressionScore {
+  r: number;
+  r2: number;
+  chi2: number;
+  rmsd: number;
+}
+
+export interface Slope extends CalculationLimits {
+  slope: number;
+  score: RegressionScore;
+  units?: string;
+}
diff --git a/todo/general/ValueXY.d.ts b/todo/general/ValueXY.d.ts
new file mode 100644
index 0000000..1c381a9
--- /dev/null
+++ b/todo/general/ValueXY.d.ts
@@ -0,0 +1,9 @@
+import { Value } from "../../src";
+
+export interface ValueXY {
+  x: Value;
+  xLabel: string;
+  y: Value;
+  yLabel: string;
+  index: number;
+}
diff --git a/todo/spectra/IV/IV.d.ts b/todo/spectra/IV/IV.d.ts
new file mode 100644
index 0000000..394e884
--- /dev/null
+++ b/todo/spectra/IV/IV.d.ts
@@ -0,0 +1,23 @@
+import { MeasurementBase } from '../MeasurementBase';
+import { MeasurementVariable, Value } from '../../../src'
+import { BaseDerivedProperty } from '../core/BaseDerivedProperty';
+import { ValueXY } from '../../general/ValueXY';
+import { Slope } from '../../general/Slope';
+import { Integral } from '../../general/Integral';
+import { VariablesRecord } from '../../utils/VariablesRecord';
+
+export interface IV extends MeasurementBase {
+  settings?: {
+    /** Area to calculate the density values */
+    surfaceArea?: Value
+  }
+  derived?: {
+    thresholdVoltage?: ValueXY;
+    subthresholdSlope?: Slope;
+    resistanceOn?: Slope;
+    capacitanceIntegral?: Integral;
+    meta?: Record<string, BaseDerivedProperty>;
+  };
+
+  variables: VariablesRecord<MeasurementVariable>;
+}
diff --git a/todo/spectra/MeasurementBase.d.ts b/todo/spectra/MeasurementBase.d.ts
index d241883..adc1c7a 100644
--- a/todo/spectra/MeasurementBase.d.ts
+++ b/todo/spectra/MeasurementBase.d.ts
@@ -2,14 +2,12 @@ import { DataSource } from '../general/DataSource';
 import { HTMLString } from '../general/HtmlString';
 import { Instrument } from '../general/Instrument';
 
-import { BaseDerivedProperty } from './core/BaseDerivedProperty';
-
-/**Generic type for the result of a measurement, e.g., a spectrum or result from a crystallographic experiment */
+/** Generic type for the result of a measurement, e.g., a spectrum or result from a crystallographic experiment */
 export interface MeasurementBase {
-  /**Instrument that was used to perform the measurement */
+  /** Instrument that was used to perform the measurement */
   instrument: Instrument;
   /** Description of the source of the data*/
   dataSource?: DataSource;
-  /**Results obtained from analysing the data */
+  /** Results obtained from analyzing the data */
   remarks?: HTMLString;
 }
diff --git a/todo/utils/VariablesRecord.d.ts b/todo/utils/VariablesRecord.d.ts
new file mode 100644
index 0000000..0904740
--- /dev/null
+++ b/todo/utils/VariablesRecord.d.ts
@@ -0,0 +1,3 @@
+import { OneLetter } from "../../src";
+
+export type VariablesRecord<DataType, Obligatory extends string = 'x' | 'y'> = Partial<Record<OneLetter, DataType>> & Record<Obligatory, DataType>;