Not that I am arguing with anyone, but my flight computer, knows my flap position, it also knows when I dump water and for how long (LX 90xx). I have in the profile the empty weight of glider and my weight with chute. True I need to set the amount of ballast and bugs. The argument that if the pilot does not enter the glider weight the results are wrong. It is nearly impossible to design idiot proof equipment, because they always make better idiots. As for software vs direct measure, there is a reason I do not have a vario named after me. Good discussion though and perhaps someone with a sharp pencil will design such a unit.