交易所里的Posion 和 balance

position是指 头寸

头寸就是资金
头寸（position）是一个金融术语，指的是个人或实体持有或拥有的特定商品、证券、货币等的数量。汉语将其翻译为“头寸”，源于旧社会作为货币的“袁大头”每十个摞起来为一寸  。
头寸是一种市场约定，承诺买卖合约的最初部位，买进合约者是多头，处于盼涨部位；卖出合约者为空头，处于盼跌部位

balance指余额

balance原意是两个测量盘。那么或许可以引申为剩下的一盘子东西，就是余额了

early 13c., "apparatus for weighing," from Old French balance (12c.) "balance, scales for weighing,
" also in the figurative sense; from Medieval Latin bilancia, from Late Latin bilanx, from Latin (libra)
 bilanx "(scale) having two pans," possibly from Latin bis "twice" + lanx "dish, plate, scale of a balance." 
The accounting sense is from 1580s; the meaning "general harmony between parts" is from 1732; sense
 of "physical equipoise" is from 1660s. Balance of power in the geopolitical sense is from 1701. Many figurative 
uses (such as hang in the balance, late 14c.), are from Middle English image of the scales in the hands of 
personified Justice, Fortune, Fate, etc.