Vinegar change the P H of the product it will cut through oily deposits on glass and does not leave a sediment on the glass The vinegar helps it spread better,its better for first cleans on w f p AS IT RINSES OF EASER. i Have a formula I use on first clean and UPVC but every one goes mad when I tell them so I will keep it to myself.ITs the lack of chemistry understanding that drives them nuts and the B/s the government tell us.