函数中的VBA语法错误从另一个函数返回值（带可选参数）

Question

对于对具有可选参数的函数的函数的调用，我遇到语法错误。在这些条件下，文档中列出了有关语法错误的各种方案，但我没有看到我理解在这里应用的方案。有人可以帮我理解为什么这个调用语法不好？我在没有Call语句的情况下尝试了另一种形式但是也没有用。这是以克为单位的tometric调用。

以下是代码：

' Grams -- convert ounces or pounds and ounces to grams.
' This wrapper calls function tometric flagging conversion to grams. If grams
' is called with one value, amt_x represents the number of ounces to convert
' and amt_y is set to zero as a flag. If called with two values, amt_x and
' amt_y represent the number of pounds and ounces to convert. Grams returns
' the number of grams calculated by tometric, which does the calculation.

Public Function grams(amt_x As Double, Optional amt_y As Double = 0) As Double
    ' ****** The following generates a syntax error
    grams = call tometric("g", amt_x, amt_y)
End Function

' tometric -- Convert ounces or pounds and ounces to either grams or kilograms.
' The Unit argument specifies whether to convert to grams ("g") or kilograms
' ("kg"). The amounts to convert are either ounces or pounds and ounces, as
' documented in the grams function.

Public Function tometric(unit As String, amt1 As Double, Optional amt2 As Double = 0)
    If unit <> "kg" And unit <> "g" Then
        MsgBox "unrecognized conversion unit specified: " & unit
    Else

        ' If there are three arguments, amt1 = pounds and amt2 = ounces, else
        ' amt1 = ounces

        If amt2 = 0 Then
            tometric = WorksheetFunction.Convert(amt1, "ozm", unit)
        Else
            tometric = WorksheetFunction.Convert((amt1 * 16) + amt2, "ozm", unit)
    End If
End Function