Hi,
In your example, if yazi_reg is 0 harf_reg will be set to 30 when executing the LOOKUP statement. If yazi_reg is 1 harf_reg will be set to 72 (which is the ASCII code for 'H') and so on.
In other words, harf_reg will be set to the value within the brackets "pointed at" by yazi_reg

LOOKUP works with constants stored an compile time. You can not execute LOOKUP on an array of bytes, and there's really no need to. You can just do something like myByte = myArray[n] where n is the location in the array you want to "get".

/Henrik.