BlockHead is a visual calculator, for the addition and subtraction of multiple-digit whole numbers. You type in the numbers to be combined, and BlockHead draws each one as a set of place-value "blocks" (like Cuisenaire rods). For example, the number 528 is represented by a 5-block in the hundreds column, a 2-block in the tens column, and an 8-block in the ones column.

You perform the addition or subtraction operation by drag-and-drop-ing the blocks:

* For addition, you drag the blocks for both addends to an "answer" area, where they are automatically stacked. If the stack height is 10 or more, a "carry" button appears; clicking the button performs the carry as an animation.

* For subtraction, you drag the blocks for the smaller number on top of the blocks for the larger number. BlockHead automatically "chops off" the correct amount from the larger block. Sometimes, you need to click an "exchange" button, in order to build a stack that is large enough to be "chopped off".

At the source code level, you can:

* control the number of columns in each number
* change the number base (any base from 2 to 10)

Support

Support for this activity is provided by the developer at jjposner at optimum dot net

Version 7, 23-Sep-2009

1. Includes a help facility:

* The "Help" button now toggles between "Show Help" and "Hide Help".

* Showing help entails displaying a help panel instead of the blocks panel.

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