What is upgrade spending and more importantly, why does it decrease?

starcraft-2

Solution 1:

Upgrade spending tracks your tech in general, not just "upgrades". So if you build a roach warren, it will show in this graph. If you then lose the roach warren, the graph will reflect this loss in tech.

Related

What is the best way to identify consumables?
Easiest place to find loot Goliaths and make god-liaths
How to find out who controls the courier?
How to throw enemies into a pit in Dwarf Fortress
Do the systems always follow the same pattern?
Do drives fragment, and if so is there a way to defragment them automatically?
How do I drink milk in Feed The Beast?
Where is the best place for demon hunting? (kill 100,000 demons achievement)
What would attract an Enderman into a pit?
How much does Town Hall Level 9+ reduce the loot from opponents?
What's the difference between killstreak, specialized killstreak, and professional killstreak weapons?
Do you need to be a werewolf to complete the Companions quests?