How can I calculate the number of hours between two date and time fields?

To calculate the number of hours between two date and time fields, add a formula field and specify the formula expression as ((To_Date - From_Date) / (1000 * 60 * 60))

form  Sample
{    
    FromDate
    (
        type  =  datetime
    )

    ToDate
    (
        type  =  datetime
    )

    Hours
    (
        type  =  formula
        value  =  ((To_Date - From_Date) / (1000 * 60 * 60))
    )
}