diff --git a/src/ZenithAngleCalc.jl b/src/ZenithAngleCalc.jl
index 33b5447..2e93110 100644
--- a/src/ZenithAngleCalc.jl
+++ b/src/ZenithAngleCalc.jl
@@ -37,7 +37,22 @@ function get_Δt_years(
     return FT(datetime2julian(date) - datetime2julian(date0)) / days_per_year
 end
 
+"""
+    distance_declination_hourangle(
+        date::DateTime,
+        date0::DateTime,
+        (ϖ, γ, e)::Tuple{FT, FT, FT},
+        param_set::IP.AIP,
+        eot_correction::Bool,
+    ) where {FT}
+
+Returns the earth-sun distance (m), declination angle (radians) and hour angle 
+(radians), at 0ᵒ longitude, given the current datetime, epoch datetime, 
+`longitude of the perihelion at epoch`, `obliquity at epoch`, `eccentricity at epoch`, 
+and `eot_correction`.
+
 # calculate the distance, declination, and hour angle (at lon=0)
+"""
 function distance_declination_hourangle(
     date::DateTime,
     date0::DateTime,
@@ -83,15 +98,16 @@ end
 
 """
     instantaneous_zenith_angle(
-        (d, δ, η_UTC)::Tuple{FT, FT, FT},
+        d::FT,
+        δ::FT,
+        η_UTC::FT,
         longitude::FT,
         latitude::FT,
-        param_set::IP.AIP,
     ) where {FT}
 
-Returns the zenith angle, azimuthal angle and Earth-Sun distance
-at a particular longitude and latitude given Earth-Sun distance, declination angle, 
-and hour angle at longitude = 0.
+Returns the zenith angle (radians), azimuthal angle (radians) and Earth-Sun distance (m)
+at a particular longitude (degrees) and latitude (degrees) given Earth-Sun distance (m), 
+declination angle (radians), and hour angle (radians) at 0ᵒ longitude.
 
 """
 function instantaneous_zenith_angle(