None of the aviation industry bluebooks may be expected to give the simple calculation accuracy typical of the US automotive industry books such as Automobile Blue Book, or Kelley Blue Book. A number of issues contribute to the difficulty in presenting a clear figure for a make/model/year, such as lack of central reporting of aircraft sales for either tax or license requirements, the complexity of individual aircraft value calculations, the timing of sales (long timeframes from offer to closing during which time the market can go up or down substantially), multiple synchronous closings for jet aircraft in particular, international currency sales, and non-disclosure-of-price terms included in many transaction documents.[2]