Print a single record report from a button on a form

Hello, 

I am converting a database from Paradox to Access. I have limited Access experience. I am trying to print a single record on a report launched from a button on the form. I duplicated some code I found on another forum changing the form name, report name and field. When I press the button the report launches but it is blank, no output. The code I used is below. UNIT is the data field for the data and each record has a unique number.  UNIT is not the primary key. 

Option Compare Database

Private Sub Command394_Click()

End Sub

Private Sub command399_Click()
DoCmd.OpenReport "FLEET-MACHINE DATA SHEET", acViewPreview, , _
"[UNIT]=Forms!frmFLEET_MASTER_DEVELOP"
End Sub

Private Sub Print_Machine_Detail_Click()

End Sub

Blank output below.

I tried modifying the code:

Option Compare Database

Private Sub Command394_Click()

End Sub

Private Sub command399_Click()
DoCmd.OpenReport "FLEET-MACHINE DATA SHEET", acViewPreview, , _
"[UNIT]=Forms!frmFLEET_MASTER!UNIT" '""
End Sub

Private Sub Print_Machine_Detail_Click()

End Sub

This launches a box which allows me to input the unit # and output to the report. I would like to code it so the user does not have to input any variable to run the report.