Stand with your back against a wall and feet close together (narrow stance). Walk your feet forward and slide down until your knees form about a 90° angle and thighs are roughly parallel to the floor. Press your back into the wall, keep your core engaged, and hold the position. Breathe steadily and hold for the desired time, then push through your heels and slide back up the wall to standing.
Log your wall sit (narrow stance) sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.