One way to learn a new "language" is to start trying to speak it. So have at it and we'll help correct you if needed.
Define a global field for your height. This is done by opening field options in Manage | database | fields by doubleclicking the field and selecting this option on the storage tab of the field options dialog.
Now your calculations will all refer to this global field from every record and thus will compute the same value in every record.
Thanks for the instruction. Now, onto learning new things! :)