UK Diminishing Returns

[thomas brown]

Hi, I'm looking at a case study based on wed developments and changes. These items bring in new orders/sales when introduced but as users become used to the change the value of the impact diminishes. For example a new change brings in 100 orders per month after 3 months you expect 66, 6 months 33 then after 9 months expect that the value of the change has fully diminished/decayed. Have assumed this level of decay as the case I am looking at is a fast paced, competitive environment where things change quickly. Has anyone got examples of diminishing returns in the tech industry (google etc) or advice on a more appropriate model? Haven't been able to find any examples & existing accountancy rules on depreciation etc do not seem to fit it.