  Results from the NA49 experiment at the CERN SPS are presented on
event-by-event transverse momentum and multiplicity fluctuations of charged
particles, produced at forward rapidities in central Pb+Pb interactions at beam
momenta 20$A$, 30$A$, 40$A$, 80$A$, and 158$A$ GeV/c, as well as in systems of
different size ($p+p$, C+C, Si+Si, and Pb+Pb) at 158$A$ GeV/c. This publication
extends the previous NA49 measurements of the strongly intensive measure
$\Phi_{p_T}$ by a study of the recently proposed strongly intensive measures of
fluctuations $\Delta[P_T, N]$ and $\Sigma[P_T, N]$. In the explored kinematic
region transverse momentum and multiplicity fluctuations show no significant
energy dependence in the SPS energy range. However, a remarkable system size
dependence is observed for both $\Delta[P_T, N]$ and $\Sigma[P_T, N]$, with the
largest values measured in peripheral Pb+Pb interactions. The results are
compared with NA61/SHINE measurements in $p+p$ collisions, as well as with
predictions of the UrQMD and EPOS models.
