Mass-per-charge spectrum of heavy pickup ions (Δm/q = 0.4 amu/e) observed by PLASTIC on board STEREO A. The data was accumulated for a period of 2400 days, beginning in March 2007, and C⁺ velocities of w_sw,C⁺> 0.2 (open circles). A mass-per-charge model (dashed black line) was fitted to the data to obtain the absolute abundances of C⁺, N⁺, O⁺, Fe³⁺, Ne⁺, Mg⁺, and Fe²⁺ in terms of instrumental count rates. An exponential model was included to estimate and incorporate the influence of instrumental background to the mass-per-charge spectrum between 10 <m/q< 35 amu/e.