New Math

I'm fairly new here but could someone explain this new math that CC seems to be using? 

If I tell it I burned 300 calories...it only adds 210 calories to my burn meter.

When I look at the 7 day totals, I presume it is telling me my caloric intake over the last 7 days since the number does not match any of the days.  But when I do the math I learned WAAAAAAAAAY back in the day.....I get a different total. 

Is the whole site that way?  The calorie count and burn is already a bit of a guesstimate as it is.  If the math is all wrong then you REALLY are not going to get a good guideline to follow.  I realize if it is always off the same then it can, in essence, be accurate.  But I don't intend to live my days on this site.  It's great for a guideline but eventually I'd like to step out on my own without the site as a crutch.  If the numbers are THAT far off then what I learn here will not really help so much  later.  If I learn that my 'magic number' is 1550 and that walking X times a week works this way or that and the numbers are wrong...it will NOT work for me without the CC calculator. 

Does anyone one know why it is like this?  And is there a CC calculator I can buy out there somewhere?...LOL

Thank you so much for all of your input.  It's been a great help. (insert 'dripping with sarcasm' smiley here)