diff --git a/definitions/grib1/2.98.170.table b/definitions/grib1/2.98.170.table
index 3eb89b6cf..64a66e8f2 100644
--- a/definitions/grib1/2.98.170.table
+++ b/definitions/grib1/2.98.170.table
@@ -1,7 +1,7 @@
 # This file was automatically generated by ./param.pl
-1 1 SPI03 Standardised precipitation index valid for 3 months (dimensionless)
-2 2 SPI06 Standardised precipitation index valid for 6 months (dimensionless)
-3 3 SPI12 Standardised precipitation index valid for 12 months (dimensionless)
+1 1 SPI03 Standardised precipitation index valid for the last 3 months (dimensionless)
+2 2 SPI06 Standardised precipitation index valid for the last 6 months (dimensionless)
+3 3 SPI12 Standardised precipitation index valid for the last 12 months (dimensionless)
 129 129 Z Geopotential (m**2 s**-2)
 130 130 T Temperature (K)
 131 131 U U component of wind (m s**-1)