SUBROUTINE AnnulusPropertyCalculator (md, den, pre, tem)
    
    !!! This subroutine gets location of a guage or an observation point and determines information of that point such as pressure, density, velocity and temperature later.
    use PressureDisplayVARIABLESModule
    USE Fluid_Flow_Startup_Vars
    USE MudSystemVARIABLES
    USE FricPressDropVarsModule
    USE CDrillWatchVariables
    
    IMPLICIT NONE
    INTEGER, intent(in) :: md  ! input
    REAL(8) :: TVD
    real(8), intent(inout) :: den  ! output
    real(8), intent(inout) :: pre  ! output
    real(8), intent(inout) :: tem  ! output
    
    
    INTEGER :: ilocal
    
    CALL TVD_Calculator(md * 1.d0 , TVD)
    
    IF (md <= INT(FinalFlowEl(FricPressDropVars%AnnulusFirstEl)%StartX)) THEN         !! mouse pointer is in the annulus space
        DO ilocal = FricPressDropVars%AnnulusFirstEl , FricPressDropVars%AnnulusLastEl
            IF (INT(FinalFlowEl(ilocal)%EndX) <= md)   EXIT
        END DO

    ELSE IF (md > INT(FinalFlowEl(FricPressDropVars%NumbEl)%EndX)) THEN       ! mouse pointer is in the open hole space
        DO ilocal = FricPressDropVars%OpenholeFirstEl , FricPressDropVars%NumbEl
            IF (INT(FinalFlowEl(ilocal)%EndX) <= md)   EXIT
        END DO

    ELSE
        WRITE (*,*) ' Error in calculating annulus observation point '
    END IF
    pre = FinalFlowEl(ilocal)%StartPress - (FinalFlowEl(ilocal)%StartX - md) * FinalFlowEl(ilocal)%dPdLfric &
                                - (FinalFlowEl(ilocal)%StartTVD - TVD) * FinalFlowEl(ilocal)%dPdLGrav
    !write(*,*) ' md, ilocal', md, ilocal
    !WRITE (*,*) ' FlowEl dPdLfric , dPdLGrav', FlowEl(ilocal)%dPdLfric , FlowEl(ilocal)%dPdLGrav
    
    den = FinalFlowEl(ilocal)%Density
        
    !tem = 500
    
    
    END SUBROUTINE