diff --git a/pulseox.md b/pulseox.md
index 465af72a8c9d3d1051ecf0746411bc53b13461cd..d4076fa2e747a29090738729ff6404dabd8e3d06 100644
--- a/pulseox.md
+++ b/pulseox.md
@@ -68,3 +68,5 @@ A few paths exist that may be worth pursuing, given the aforementioned concerns:
 - Develop a calibration system that can be easily manufactured and deployed based on fundamental principles, i.e. one that does not need to be _itself_ calibrated. One could build a spinning hollow clear plastic wheel with two chambers and controlled thickness, with the chambers filled with various concentrations of a solution whose absorption spectrum closely matches that of blood at a given oxygenation level. The wheel would be spun to simulate the heartbeat, and different wheels would represent different SpO<sub>2</sub> values. The solution could be accurately mixed using basic laboratory equipment, such as a scale or a pipette.
 - Design an automated calibration system that uses a camera and optical character recognition to gather SpO<sub>2</sub> values from a commercial or clinical instrument and build a calibration table for the low-cost device while it is simultaneously clipped to the patient. Caregivers could "train" the low-cost device prior to patient discharge so they can self-monitor for flare-ups or subsequent respiratory ailments.
 - Develop a methodology for cheaply and accurately characterizing LEDs and other components in the low-cost sensor, so that a master calibration file from a clinical study can be propagated to other devices as is done by traditional manufacturers. 
+
+In all cases, a reasonable first step is to design and prototype a sensor with sufficient performance to measure $`R`$, the O<sub>2</sub>Hb / Hb ratio discussed above.