In Delphi, you cannot do math with generic types, as you will get "E2015 Operator not applicable to this operand type" because there is no way to constraint the generic type to be floating point or ordinal.

AxisUnit.pas

unit AxisUnit;

interface

type
  TAxis<T: record> = record
    fMin, fMax, fRange: T;
    fStart, fEnd, fExtent: single;
    function CalcCasted( const AScalar: T ): single;
    function CalcPlain( const AScalar: T ): single;
  end;

implementation

function TAxis<T>.CalcCasted(const AScalar: T): single;
var
  Offset: single;
  NormalisedOffset: single;
  ScaledOffset: single;
begin
  // First 2 lines give the same error: E2089 Invalid typecast
  Offset := single(AScalar) - fMin;
  NormalisedOffset := Offset / single(fRange);
  ScaledOffset := NormalisedOffset * fExtent;
  Result := fStart + ScaledOffset;
end;

function TAxis<T>.CalcPlain(const AScalar: T): single;
var
  Offset: T;
  NormalisedOffset: T;
  ScaledOffset: T;
begin
  // All 4 lines give the same error: E2015 Operator not applicable to this operand type
  Offset := AScalar - fMin;
  NormalisedOffset := Offset / fRange;
  ScaledOffset := NormalisedOffset * fExtent;
  Result := fStart + ScaledOffset;
end;

end.

DelphiMathAndGenerics.dpr

program DelphiMathAndGenerics;

uses
  AxisUnit in 'AxisUnit.pas';

var
  rXAxis: TAxis<TDateTime>;
  rYAxis: TAxis<single>;

begin
end.