diff --git a/here/README.md b/here/README.md
index 4907ba353..4294c2a7e 100644
--- a/here/README.md
+++ b/here/README.md
@@ -106,8 +106,8 @@ Historical data are acquired through the Traffic Analytics download portal. Data
 | stddev | numeric(4,1) | | standard deviation of the observed speed(s) |
 | min_spd | integer | | Observed minimum speed |
 | max_spd | integer | | Observed maximum speed |
-| pct_50 | integer | | Observed median speed |
-| pct_85 | integer | | Observed 85th percentile speed - use with caution as sample sizes (of vehicles) are very small within 5-minute bins |
+| pct_50 | integer | | Median speed. Likely to have been interpolated between adjacent values rather than actually observed in the sample! |
+| pct_85 | integer | | 85th percentile speed - use with caution as sample sizes (of vehicles) are very small within 5-minute bins. This value may also be interpolated. |
 | confidence | integer | | proprietary measure derived from `stddev` and `sample_size`; higher values mean greater 'confidence' in reliability of `mean` |
 | sample_size | integer | | the number of probe vehicles traversing a segment within a 5-minute bin **plus** the number of 'probe samples' |