Model 105A has partial Bi-Directional Heat/Cool Control. This means the cooling can be modulated between full on and partial cooling. Control at set point involves "bucking" heat against partial cooling.

Model 107 has full Bi-Directional Heat/Cool Control. This means the heating and cooling can be modulated full on or off. This provides more responsive temperature control - particularly at moderate temperatures - as shown in the chart below.

This chart shows the control dynamics when cooling down to a 23.0°C set point. The 105A undershoots to 21.9°C and takes nearly 10 minutes to stabilize after crossing 24°C. The 107 stabilizes to within 0.3°C of set point in approximately 1 minute. The resolution on this chart is expanded - minor perturbations represent 0.1°C.