  For negative ion beam sources there are several methods of measuring the
accelerated beam current, most commonly electrical measurements at the power
supply and calorimetric measurements. On SPIDER, the ITER Heating Neutral Beam
full-scale beam source prototype, electrical measurements at the acceleration
grid power supply (AGPS) are complemented by polarizing the diagnostic
calorimeter STRIKE to provide an additional electrical measurement of the
accelerated current. This is in addition to the calorimetric measurements
provided by STRIKE. These diagnostics give differing measurements of the beam
current. Exploiting the reduced number of open apertures on SPIDER a new beam
diagnostic has been installed to measure the individual beamlet currents
directly. The so called Beamlet Current Monitor (BCM) has been used to measure
the current of five beamlets during the most recent SPIDER campaign. This work
compares the BCM current to the electrical measurements at the AGPS and STRIKE.
The average BCM current agrees well with the STRIKE electrical measurements,
indicating that the AGPS overestimates the beam current. The individual
beamlets are compared to the STRIKE calorimetric measurements, showing similar
current trends with the source parameters.
