I believe that is the correct application of the equity method.
Consider, Company A invests in Company B.
Company B's balance sheet shows:
Assets 100
Liabilities 90
SE 10
Company A pays 6 to acquire 40% of Company B, which based on Company B's books is worth (100-90) * 40% = 4.
In other words, Company A's investment implies that Company B's net assets have a fair value greater than what is currently recorded on Company B's books. For example, instead of being worth 100, total assets might be worth 105 [(105-90) * 40% = 6].
If Company A had acquired enough of Company B to consolidate, Company B's net assets at the time of acquisition would be revalued at fair value and any remaining difference would be accounted for as Goodwill.
In the case where Company A has not acquired enough of Company B to consolidate, there is no explicit revaluation of Company B's assets to fair value. However, we don't want to just ignore the difference, so we kinda sorta pretend like a consolidation has taken place. Some or even all (common for textbook problems) of that difference can be attributed to Company B's depreciable assets having fair values higher than their carrying values on Company B's books.
Now, if those depreciable assets had been recorded on Company B's books at their higher fair value, depreciation recognized by Company B over the same useful life would be higher, and this would result in a greater depreciation expense and lower net income, and therefore lower investment income recognized by Company A and a smaller debit to Company A's investment in Company B. So Company A accounts for this additional depreciation itself (note that in this particular context it is also sometimes called amortization). The implication being that at the end of the assets' useful lives, their fair value and their carrying value on Company B's books is now the same.
Given the above, the adjusting entry looks like you might expect it would, reversing some of the income previously recognized:
Dr. Income from investment in Company B XXXX
Cr. Investment in Company B XXXX
In the case of your sim, the implied fair value of the equipment is $100,000 higher than the book value. The investor depreciates its share of that difference over the 5-year remaining useful life.
That's always been my understanding of it anyway. Somebody feel free to correct me if I'm wrong.
ASC 323-10-35 is where it's addressed in the codification.