The relative productivity of factor

The relative productivity of factors might changes (e.g. if technical developments improved the productivity of capital, firms should substitute capital for labour to take advantage of its increased relative productivity)
Different technologies might become possible at output levels greater than 100 units. (e.g. at low output levels it might be unprofitable to consider high levels of automation, yet such productive methods could be introduced at higher levels of output. Highly automated car production linesprovide an illustration)
Increasing output beyond 100 units requires the employment of more factors. In the short run (see below ) it may be impossible to obtain more of both factors (e.g. additional capital may be unavailable and the firm can only increase output by employing more lobour with a fixed supply of capital. If so, the ratio of capital to labour falls)
The variability of factors is an important concept. The economist defines three distinct time when the adjusts the adjusts its productive capabilities: