....ASICS is dead thing as i managed to calculate?
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it increases every 2016 blocks. and 1 block must be mined every 600 seconds. are those 600 seconds final?
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If you have to ask your second question then I suspect that the calculation that you made as part of your first question is wrong.
Difficulty is re-calculated every 2016 blocks to give a new difficulty. That new difficulty is used from that point on and is calculated to allow a block to be solved every 600 seconds. It is a self adjusting mechanism but is only correct when it is calculated as it is impossible to know how many new miners are being added and how many old miners have been removed or stopped working.
As miners get faster and more numerous so the difficulty increases but at some point this will level because at some point the money being earned will not warrant the cost of the miner and the electricity to power it, so miners less miners will be brought and more will be removed or not replaced when they stop.
You can buy miners now whilst the difficulty is rising fast, buy at some point in the future or just but bitcoin to invest. Each is a valid proposition but there is no magic 8 ball to tell you which one to choose, you have to workout what is effective for you and balance that against the risk that you are willing to take with your money.
One thing is certain though, if you are not in the you risk nothing but also gain nothing.