I've been logging data from BTC-E for a couple of months now and am writing my own charting app for personal use. I've been stumped for a while now on what the difference between "vol" and "vol_cur" is and how to determine the volume for any given interval I want (1min, 60min, 2month, etc):
https://btc-e.com/api/2/ltc_usd/ticker
{"ticker":{"high":11.976,"low":11.35,"avg":11.663,"vol":2147898.06418,"vol_cur":184074.26807,"last":11.35,"buy":11.35,"sell":11.32,"updated":1396883318,"server_time":1396883319}}
Subtracting the "vol" values from the end of my interval to the start sometimes yields negative numbers:
id | timestamp_open | timestamp_close | open | close | high | low | volume
----+---------------------+---------------------+----------+---------+----------+----------+--------------
2 | 2014-02-15 18:00:00 | 2014-02-15 18:30:00 | 16.05385 | 15.9761 | 16.0675 | 15.9761 | -62044.90371
3 | 2014-02-15 18:30:00 | 2014-02-15 19:00:00 | 15.9761 | 16.049 | 16.05385 | 15.94642 | -40416.73599
4 | 2014-02-15 19:00:00 | 2014-02-15 19:30:00 | 15.94652 | 16.002 | 16.05385 | 15.935 | 32560.39743
5 | 2014-02-15 19:30:00 | 2014-02-15 20:00:00 | 16.002 | 16.05 | 16.05 | 16 | 31619.54125
6 | 2014-02-15 20:00:00 | 2014-02-15 20:30:00 | 16.03175 | 15.999 | 16.0532 | 15.9 | -10595.7155
7 | 2014-02-15 20:30:00 | 2014-02-15 21:00:00 | 15.999 | 15.997 | 15.999 | 15.94 | 61109.18234
8 | 2014-02-15 21:00:00 | 2014-02-15 21:30:00 | 15.997 | 16.132 | 16.25 | 15.997 | -33001.28287
The price did not close down so it is not representative of volume indicative of selling; how do I properly calculate the volume for an interval?