T = t1.past(MINUTE).average;

THERMISTORNOMINAL = 10000;

 // temp. for nominal resistance (almost always 25 C)
TEMPERATURENOMINAL = 25;

// The beta coefficient of the thermistor (usually 3000-4000)
BCOEFFICIENT = 3435;

// the value of the 'other' resistor
SERIESRESISTOR = 14910;

average = 1023.00 / T  - 1.00;

average = SERIESRESISTOR / average;

steinhart = average / THERMISTORNOMINAL; // (R/Ro)
steinhart = Math.log(steinhart); // ln(R/Ro)
steinhart /= BCOEFFICIENT; // 1/B * ln(R/Ro)
steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
steinhart = 1.0 / steinhart; // Invert
steinhart -= 273.15; // convert to C

return steinhart ;

Trouble is that when even for the past one hour where there is **NO **t1 value received, the average function still returns the average based on whatever was stored earlier. I was expecting that in case of no data, the average function based on time would return a NULL.

Any thoughts / suggestions ?