if you know maths, this should be easy.
if a alt coins wants to be valued at lets say $1, then if bitcoin goes from $500 to $700 (40% rise) then the altcoin would change from
0.00200000 to then be 0.00142857 to remain at a $1 value
need i explain more?
This isn't true for instance bitcoin was down to 540 while Betacoin went up to 0.00006000 then bitcoin rised and now Bet is at 0.00001300 a very huge drop.
Like 2/3rds of the alts did this.
Worldcoin was at .0007 for a while, now sitting at .00012.
When it got down to .0002 I thought "No way, surely it will go back up a little" and here it is approaching .0001. My coins are pretty much worthless.
This "$ value" math doesn't apply all of the time. It applies to Litecoin, some of the time. The rest of the alts almost always go down against BTC when BTC goes down against the dollar. They sort of, double lose. I've seen Litecoin go both ways depending on how the market feels that day.