Here is mine BTC index. This is first propose, so nothing special here.
Data from coinmarketcap. Index counted as a simple average.

# Source Pair Volume(24h) Price Volume(%) DATE & TIME request
2 Bitfinex BTC/USD $497 589 000,00 $9 250,00 6,73 04.02.2018 0:52:29
4 Binance BTC/USDT $257 805 000,00 $9 221,14 3,49
7 Bitstamp BTC/USD $160 078 000,00 $9 235,99 2,17
19 Kraken BTC/USD $74 959 600,00 $9 177,40 1,01
22 HitBTC BTC/USDT $61 812 700,00 $9 256,26 0,84
25 Poloniex BTC/USDT $51 543 300,00 $9 222,20 0,7
26 Bittrex BTC/USDT $51 241 800,00 $9 202,51 0,69
Total $1 155 029 400,00 $9 223,64 15,63

Also i've added BTC prices from all exchanges to compare deviation from index.

Also i've added fibonacci as a propose to analyse index, also here is price corridor.

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