↩ 🔵 🔵 🔵 ❪∂_❫ High-Energy Astrophysics Subs ○ Chi-Squared (χ²=Σ₍C₍I₎-Cₚ₍I₎₎²∕σ₍I₎²) ○￩ᴴᴱᴬ Photon Counts (C) ○◂ Observed Counts (C₍I₎) ○◂ Instrument Channel (I) ○◂