Talk:Gems/@comment-24457062-20140218191406

Been looking at the impact of gems on repair costs and income when you have 3 Oracles and 3 Totems. This interested me because I was trying to work out the relative merits of putting an Emerald versus a Topaz into a high income/high repair cost building and one which has a high repair cost relative to the income received on collection. In my case it was the Thanks Captain building - which at Level 5 has a repair cost factor that is around 16 times its income collection (at 100% income).

At first I thought putting in a Topaz (14%) looked good relative to an Emerald (10%) because I assumed a Topaz worked off the original repair cost (pre-Oracle cost). But now after looking at my buildings with gems inserted – I find that a Topaz works off the post-Oracle repair cost – and that the impact of a Topaz is equivalent to a 9.8% reduction on the original repair costs. As an illustration: if you have 3 Oracles and the original repair cost (pre-Oracles) was say $100... you would get 30% (3 times 10%) or $30 off the repair cost, so the repair cost becomes $70. Now if you add a Topaz into the building...it works off the post-Oracle repair cost i.e adding a Topaz (14% off the $70 repair cost) will result in a cost reduction of $9.8 (or 9.8%).

Emeralds also work off the post-Totem income - but in a positive direction. An Emerald (10%) works out to be around a 13% increase on original income (pre-Totem income).

I know the absolute impact in dollar terms will depend on when you collect and if whether it is 70% to 100% of maximum income. I did a quick calculation and assumed that on average I collect at 80% of average income, with an average of 1 breakdown over 14 collections. Even with the relatively high repair cost factor (16x income) of the Captains - it is still more profitable to put in an Emerald into my Captains.

Does this seem right - or have I missed something in my analysis?