Randy Marsh's TMI formula in PowerShell

Get-TMI.ps1

function Get-TMI {
    <#
    .SYNOPSIS
    Calculates the TMI of a given object.
    .DESCRIPTION
    Calculates the TMI of a given object.
    .PARAMETER Length
    The length of the object
    .PARAMETER Diameter
    The diameter of the object
    .PARAMETER Weight
    The weight of the object
    .PARAMETER Girth
    The girth of the object
    .PARAMETER AngleOfShaft
    The angle of the shaft
    .PARAMETER Average
    If set, the average of the TMI will be returned when multiple TMIs are provided via the pipeline.
    .PARAMETER Sum
    If set, the sum of the TMI will be returned when multiple TMIs are provided via the pipeline.
    .PARAMETER StandardDeviation
    If set, the standard deviation of the TMI will be returned when multiple TMIs are provided via the pipeline.
    .EXAMPLE
    Get-TMI -Length 6 -Diameter 2 -Weight 4500 -Girth 4 -AngleOfShaft 45
    .INPUTS
    System.Double
    .OUTPUTS
    System.Double
    #>
    [OutputType([System.Double[]])]
    [CmdletBinding(SupportsShouldProcess)]
    param (
        [Parameter(Mandatory, ValueFromPipelineByPropertyName)][double]$Length,
        [Parameter(Mandatory, ValueFromPipelineByPropertyName)][double]$Diameter,
        [Parameter(Mandatory, ValueFromPipelineByPropertyName)][double]$Weight,
        [Parameter(Mandatory, ValueFromPipelineByPropertyName)][double]$Girth,
        [Parameter(Mandatory, ValueFromPipelineByPropertyName)][double]$AngleOfShaft,
        [Parameter()][switch]$Average,
        [Parameter()][switch]$Sum,
        [Parameter()][switch]$StandardDeviation

    )
    begin {
        $TMIArray = New-Object System.Collections.Generic.List[double]
    }
    process {
        if ($PSCmdlet.ShouldProcess("Calculating TMI")) {
            $TMIArray.Add(
                $(
                    $($($Length * $Diameter) + $($Weight / $Girth)) / [math]::Pow($AngleOfShaft, 2)
                )
            )
        }
    }
    end {
        if ($TMIArray.Count -gt 1 -and $Average) {
            $TMIArray | Measure-Object -Average | Select-Object -ExpandProperty Average
        }
        elseif ($TMIArray.Count -gt 1 -and $Sum) {
            $TMIArray | Measure-Object -Sum | Select-Object -ExpandProperty Sum
        }
        elseif ($TMIArray.Count -gt 1 -and $StandardDeviation) {
            $TMIArray | Measure-Object -StandardDeviation | Select-Object -ExpandProperty StandardDeviation
        }
        else {
            $TMIArray
        }
    }
}