Although there are many variations of escalation clauses, all are intended to adjust rents by reference to external standards such as published indexes, negotiated wage levels, or expenses related to the ownership and operation of buildings. During the past thirty years, Landlords have developed the custom of separating the base rent for the occupancy of the leased premises from escalation rent. This technique enables the landlord to better ensure that the “net” rent to be received under the lease will not be reduced by the normal costs of operating and maintaining the property. The landlord’s definition of Operating Expenses is likely to be broad, covering most costs of operation of the building. Most landlords pass through proper and customary charges, but in the hands of an overly aggressive landlord, these clauses can operate to impose obligations which the tenant would not willingly or knowingly accept.