Entries

Not all of these might work in newer browers and def. not in all browsers

Use byte order mark to set utf8 instead of meta charset (16 bytes)
JS code in onload= (10 bytes)
Skip all use of " in html (2 bytes)
Fetch element by global js-variable set by id= (27 bytes)
Set m=Math (<num_uses - 1>
3-2 bytes)
Set font to "4 a" instead of "4px arial", but since we skip " in onload we can't have space so replace with \r (5 bytes)
Set and update varibles right in the "for (;;)" to save having to use {} and some ";" (~3 bytes)
Count down to 0 in condition part so it autostops and we save condition check (3 bytes)
Make sure ending newline is killed (1 byte)
Reuse any numeral value as many places as possible, possibly making subtle changes to the effect
= has higher priority than +=, allow you to assign static base values and add in the same step
use <condition>&&<code> instead of if ()
setInterval takes a string
Use approximate values to get away with fewer decimals
Try to reuse any drawing function as a clearing function as well
Use canvas and onclick to execute all code to avoid needing <body>-tag