Place the digits 1-8 once each in every row, column and region. A digit in a cell with a circle must be odd. A digit in a cell with a square must be even. There are invisible thermometers in this grid. Every empty cell (the 6x6 in the center) gets visited by one of those thermometers. Digits on a thermometer increase from the bulb on one end to the tip on the other end. The thermometers are orthogonally connected and don't fork or overlap. A thermometer may have length 1 if it's bulb and tip are the same cell. The difference between bulb and tip must be unique for each thermometer.