Thermican, the Slow Bolometer Monk Mug

A bolometer with heat capacity C and thermal link G has time constant τ = C/G; it warms and cools exponentially with τ, just like Newton's law of cooling: ΔT = ΔT₀ e^−t/τ, where ΔT is the temperature difference to the room, ΔT₀ its initial value, t the time and τ the time constant.

The joke: Bolometer people tune C and G; the time constant is literally slowness by design. The slogan on the mug reads τ = C/G. SLOW TO WARM, SLOW TO FORGIVE.

Source: P. L. Richards, J. Appl. Phys. 76, 1 (1994).