This application is an Imperial units and US customary units Calculator. (I call it merely 'Imperial units' from here.)
Conversion is very common, but the direct calculation keeping units is rare, I think.
I dare to limit available units only 4 kinds (length, area, volume, mass).
(I omit the units for specialist. And I limit to equip only the units those calculations may be necessary for ordinary people.
If menu categories are too many, the purpose item is buried in the menu and difficult to find.)
I designed this application with the aim of the least operation for direct calculation of Imperial units.
I warn you that the other normal conversion application may be better handy if your aim is only conversion.
This is not aiming to cover conversion result easy, because you already have the other conversion application and feel no problem for conversion purpose only.
It includes following functions these other unit converters normally do not have.
・Connection of plural units can be used in display and calculation. For example, it can calculate "2feet5inch＋6feet9inch ＝ 9feet2inch".
・Fraction input and fraction display of result. For example, 5_1/4 inch.
・Metric prefix (SI) like kilo, can be used independently from metric units and all kinds are prepared.

This application has the same merit as all other my calculation application has. The calculation result comes only by different point numeric correction.
Not all calculation finishes with getting the result. You often have the demand such as follows.
・To get results when the input is different. And the results of more various inputs.
・To get the input of the adjusted result.
This application watches a touch action to display number itself and does numerical value correction or input.
It makes simpler and easier the operation (correction, recomputation) like above cases.

(Spec)
・Every numeric of length, area, volume, mass is switchable from 3 kind formats. (Plural Imperial units connection, single demanded Imperial unit or metric unit.)
・Addition 2 sheets (4 items), Multiplication 2 sheets (4 items), 1 simple auxiliary total sheet (2 items total) are equipped.
・The touch action direct to the digit you want to change, makes numerical input or modify. It automatically calculates the results.
・Each kind of units has independent keyboard.
・Copy / paste function of a sheet or each numeric.
・2 memories
・Landscape mode display (iPhone/iPod touch: one numeric enlargement / iPad: split screen)
・iPhone/iPod touch: 10-digit display / iPad: 14-digit display (Numeric amount becomes smaller when it is accompanied by units.)
・Internal calculation operations: 16-digit decimal (Not binary floating/double) or fraction. (For error minimizing)
・Plural Imperial units connection provides choices of units connection way and choices of country difference like Imperial units and US customary units.
・Single Imperial units are shown with decimal fraction rounded by assigned digit or fraction with assigned denominator.
・Metric units are switchable from metric prefix (SI) using -2,-1, 1, 2 units like centi or not, or exponential display.
・Multitask (for i-Pad) and Handoff (2 units or more) of iOS are available.

Below units are provided.
(Length) mile, yard, feet, inch, league, furlong, chain, perch, pole, rod, link, barleycorn, pica, point, mil, thou, nmile, cable, fathom, & meter
(Area) mile², acre, yard², feet², inch², rood, chain², rod², pole², perch², section, township, & meter², are
(Volume) gallon, quart, pint, ounce, yard³, feet³, inch³, acre-feet, hogshead, bbl, bushel, peck, cup, gill, tablespoon, teaspoon, drachm, scruple, minim, & meter³, liter
(Mass) ton, hundredweight, quarter, stone, pound, ounce, drachm, grain, pennyweight, carat, tonne, troy ounce, troy pound, & gram