Lunge Machine.

Same depth every time.

The lunge is the exercise where technique slips without anyone noticing, the back knee stops a little higher with every rep once it starts to burn, and you think you trained what you planned. The padded roller sits at knee height and gives you a physical reference point, so the depth stays the same from rep to rep and from person to person. It weighs 17 kg and takes 725 × 665 mm, so you bring it out when you need it and put it away afterwards. No assembly and no plates, you use body weight, dumbbells or a bar. Seventeen kilos that keep you honest.