Who know 'the dollar bar' ?

 

As far as I know ,  there are three kind of bar,  time, tick and volumn. 

time bar--prints a bar for every x number of time, such as seconds, minutes,hours and so on.

tick bar--prints a bar for every x number of trades,If someone trades 1 contract in a transaction, that counts as one trade. If someone trades 3 contracts in a transaction, that still only counts as 1 trade. 

volume Bar--prints a bar for every x number of contracts transacted, If someone trades 3 contracts in a transaction, that counts as 3.

but when I read article https://blog.quantinsti.com/bar-types-trading/     a new kind of bar called 'dollar bar', I could not understand what the author said.  who know this kind of bar and clarify if clearly step by step? dollar bar