  We investigate the constraints on Supersymmetry arising from available
precision measurements using a global fit approach. When interpreted within
minimal supergravity (mSUGRA), the data provide significant constraints on the
masses of supersymmetric particles, which are predicted to be light enough for
an early discovery at the Large Hadron Collider (LHC). We provide predicted
mass spectra including, for the first time, full uncertainty bands. The most
stringent constraint is from the measurement of the anomalous magnetic moment
of the muon. Using the results of these fits, we investigate to which precision
mSUGRA and more general MSSM parameters can be measured by the LHC experiments
with three different integrated luminosities for a parameter point which
approximately lies in the region preferred by current data. The impact of the
already available measurements on these precisions, when combined with LHC
data, is also studied. We develop a method to treat ambiguities arising from
different interpretations of the data within one model and provide a way to
differentiate between values of different digital parameters of a model.
Finally, we show how measurements at a linear collider with up to 1 TeV
centre-of-mass energy will help to improve precision by an order of magnitude.
