I’m obsessed with fertility charting, and in my search for a Fertility Awareness app that met my needs, my husband and I created one.  The most important thing to us are our users, and their feedback is gold. We learned the hard way that women want to chart on their phones, not their computers. We want to avoid the mistake of thinking “we know best” again.  So what our customers say to us is taken very seriously. But sometimes they ask for things that we don’t want to give them!

I received a question from one of the women who downloaded our app, asking me if there was a way to enter temperatures measured to the 1/100th of a degree, (like 97.34).  She didn’t want to round to the tenth of a degree (97.3)  and risk throwing off her chart.  We thought we understood her concern.  If you’re taking your temperature every morning, you want that exact temperature to go in your chart! Rounding seems like it might throw off the chart. Right?

Well that depends on if you’re measuring in Fahrenheit or Celsius.  If you’re measuring in Celsius you must measure to .05 of a degree to catch the temperature shift.  In Fahrenheit you only need to measure to tenth (0.1) of a degree. Measuring to the hundredth (.01) of a degree is too small of an increment to make any important difference on your chart.

When charting basal body temperature (BBT), the bi-phasic temperature pattern over the course of your cycle tells you if you’re ovulating, when you’re ovulating, and the length and health of your luteal phase.  Post-ovulatory temperatures are usually around 0.3 degrees Fahrenheit higher than the preovulatory temps.  0.3 is larger than 0.01 by a factor of 30. This means that measuring to hundredths of a degree is not necessary to catch the temperature shift.

Typical Rounding Scenario

This graph shows a typical bi-phasic temperature pattern, clearly confirming ovulation.  The red line was graphed using temperatures that were accurate to the 1/100th of a degree.  The blue line is graphed using those same temperatures rounded to the 1/10th of a degree.  As you can see, the difference between the two lines is not enough to obscure a temperature shift on a chart.

We had a moment of deliberation… do we tell our user to just get a different thermometer?  Do we tell her to round her temperatures?  That didn’t seem like great customer service.

We realized that the solution is not to simply tell this woman why what she was concerned with didn’t matter.  From her perspective, rounding temperatures is a pain in the ass and she doesn’t want to do it!  THAT “pain in the ass” factor is the problem that we have to solve.  So, with this realization we decided to add the ability to chart in hundredths to our development plan.

Even though measuring to this accuracy isn’t necessary, if adding the second decimal place on our data screen makes it easier for women to get their data into the chart, we’ll do it!  We want all women to have access to the yummy benefits that are to be had from charting one’s cycle, and we are committed to removing the barriers to that, however it must be done.


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