Talk:Allowance/rewrite

Allowance (pronounced IPA: /əˈlaʊ.əns/) is an English word originating from the Old French word alouance (which evolved from Latin allaudāre, "to praise"  and from Medieval Latin allocāre, "to assign" ). The /ʌˈlaʊ/ root refers most generally to the concept of permission; an allowance in most abstract terms is an act or instance of something being allowed, that is, permitted. From this most general meaning flow many specific meanings of allowance in English, detailed in following sections.

Inevitably, the abstract concept of allowing (permitting) the expenditure or forgoing of a valuable commodity (such as money, time, space, accuracy, or quality) ends up being related to the concept of a maximum limit. Expenditure or forgoing may be allowed up to a certain maximum limit; beyond this, the permission to proceed is revoked. Thus the word allowance sometimes approaches synonymity with maximum or maximum limit.

Allowance in relation to money
Because money is ever a scarce and valuable commodity, the general concept of one person who has the authority to decide what to spend it on (that is, who has "the power of the purse") allowing another person to have some (for whatever reason) is often referred to as an allowance; some specific examples follow.

A child's allowance
A child's allowance is a small sum of money periodically given to him by his parents. His parents allow him a small amount of money each week or month. Often the parents demand that tasks (such as cleaning or sharing) be done as a condition of receiving the allowance, thus to teach the child about responsibility. A parent may also give an allowance to a child in order to teach him or her money management skills.

Construction contracting
In construction, an allowance is an amount specified and included in the construction contract (or specifications) for a certain item of work (e.g., appliances, lighting, etc.) whose details are not yet determined at the time of contracting. Typically: 1) the allowance amount covers the cost of the contractor's material/equipment delivered to the project plus all taxes less any trade discounts to which the contractor may be entitled with respect to the item of work; 2) the contractor's costs for labor (installation), overhead, profit and other expenses with respect to the allowance item are included in the base contract amount but not in the allowance amount; and 3) if the section 1 costs for the item of work are higher (or lower) than the allowance amount, the base contract amount should be increased (decreased) by the difference in the two amounts and by the change (if any) to the contractor's costs under section 2. The allowance provisions may be handled otherwise in the contract: e.g., the flooring allowance may state that installation costs are part of the allowance. The contractor may be required to produce records of the original takeoff or estimate of the section 2 costs for each allowance item. Other issues that should be considered in the contract's allowance provision are: a) may the client insist that the contractor use whomever the client wishes to do the allowance work?; and b) may the contractor charge the client back for any costs arising from a delay by the client (or client's agent) in selecting the material or equipment of the allowance in question?

Retail grocery shelf area or frontage
In retail grocery, the term “allowances” is used interchangeably with the term “slotting allowances.” Both terms refer to discounts given to retailers in exchange for either favorable placement of a product in their stores, or sometimes even the initial or continued stocking of a product. The term “slotting” refers to either slots in the warehouse for a product or space on the retail shelves. If you have ever wandered into the soda aisle of a supermarket and wondered why 20 linear feet of shelving is dedicated to products from one manufacturer, the most likely explanation is that either the manufacturer or distributor of that product, paid for that display space, either through discounts or dollars per linear foot per time period.

Engineering and machining
An allowance in relation to engineering and machining is a planned deviation between an actual dimension and a nominal or theoretical dimension, or between an intermediate-stage dimension and an intended final dimension. The unifying abstract concept is that a certain amount of difference allows for some known factor of compensation or interference. Specific examples are listed below.

Examples of engineering and machining allowances

 * Outer dimensions (such as the length of a bar) may be cut intentionally oversize, or inner dimensions (such as the diameter of a hole) may be cut intentionally undersize, to allow for a predictable dimensional change following future cutting, grinding, or heat-treating operations. For example:
 * the outer diameter of a pin may be ground to 0.0005 in oversize because it is known that subsequent heat-treatment of the pin is going to cause it to shrink by 0.0005 in.
 * A hole may be drilled 0.012 in undersize to allow for the material that will be removed by subsequent reaming.
 * Outer dimensions (such as the diameter of a railroad car's axle) may be cut intentionally oversize, or inner dimensions (such as the diameter of the railroad car's wheel hub) may be cut intentionally undersize, to allow for an interference fit (press fit).

Confounding of the engineering concepts of allowance and tolerance
Often the terms allowance and tolerance are used imprecisely and are improperly interchanged in engineering contexts. This is logical because both words generally can relate to the abstract concept of permission—that is, of a limit on what is acceptable. However, in engineering, separate meanings are enforced, as explained below.

A tolerance is the limit of acceptable unintended deviation from a nominal or theoretical dimension. Therefore, a pair of tolerances, upper and lower, defines a range within which an actual dimension may fall while still being acceptable.

In contrast, an allowance is a planned deviation from the nominal or theoretical dimension.

An example of the concept of tolerance is this: A shaft for a machine is intended to be precisely 10 mm in diameter. 10 mm is the nominal dimension. The engineer designing the machine knows that in reality, the grinding operation that produces the final diameter may introduce a certain small-but-unavoidable amount of random error. Therefore, she specifies a tolerance of ±0.001 mm ("plus-or-minus" 0.001 mm). As long as the grinding machine operator can produce a shaft with actual diameter somewhere between 9.999 mm and 10.001 mm, the shaft is acceptable. Understanding how much error is predictable in a process—and how much is easily avoidable; how much is unavoidable (or whose avoidance is possible but simply too expensive to justify); and how much is truly acceptable—involves considerable judgment, intelligence, and experience, which is one reason why some engineers are better than others.