Steel Drill
Steel Drill2 000 CROWN in game 10 GRAM in the presale
Adds +15 mining power. The power of every drill you own adds up, so a new drill does not replace the old one, it stacks on top.
Shards per hour from this drill = 15 × 300 × buildings × boosts × depth
At current competition that is about 97,24 CROWN per day, paying back in roughly 20,60 days.